Daniel Ricciardo and Sebastian Vettel find themselves as two of the leading protagonists in the 2021 Formula 1 driver market puzzle.

With Charles Leclerc penning a new long-term contract with Ferrari, Max Verstappen committing his future to Red Bull, plus Lewis Hamilton expected to extend his Mercedes stint, that leaves Ricciardo and Vettel as the biggest two remaining key players left to resolve their respective futures.

Assuming Hamilton does indeed remain at Mercedes and the reigning world champion squad also retain Valtteri Bottas in its hugely successful combination for a fifth campaign, all eyes will turn to Ricciardo.

The Australian’s big-money gamble to leave Red Bull for Renault in 2019 has not quite gone according to plan so far. Ricciardo endured a frustrating first season at Renault last year as the French manufacturer failed to meet its target of closing up to F1’s leading trio, slipping behind midfield rivals McLaren to fifth in the constructors’ championship.

Ricciardo’s ever-present smile and enthusiastic character was tested in 2019, and while he did his utmost to remain upbeat, his frustration still shone through at times. Granted, he was fully aware upon his arrival to Enstone that this was to be a long-term project and there would be no obvious likelihood of immediate success, but the progress Renault expected to make did not come.

Entering the final year of his first Renault contract, 2020 is set to be a crucial year for both parties, and the current delayed start and uncertainty amid the coronavirus crisis is doing neither side any favours with big calls set to be made.

Ricciardo needs to see a serious improvement to be persuaded to stick it out at Renault, otherwise the lure and potential opening of a top drive would prove too much of a temptation to pass up.

Time is no longer a luxury for Ricciardo, who turns 31 in July. He left Red Bull at a time when his stock as a seven-time grand prix winner was at its highest, but he is at risk of falling into mid-pack obscurity. There is already a host of younger drivers lining up as frontrunners to challenge Hamilton’s current authority at the top of F1, and Ricciardo will only fade off that radar if things do not change.

On the eve of the season, Ricciardo admitted that he had already expected to be at least a one-time world champion by this stage of his career.

“After my year in 2014, if I then look at 2020, I would have expected a world title or three,” Ricciardo said.

“So from 2014 onwards I’m certainly not surprised, If anything I’m probably a little bit underwhelmed.

“But from 2011 to now to have the impact I’ve had on the sport and where I’ve put myself, for sure I’m happy and proud. But I’m certainly not there yet and not done.

“I’m pretty happy with the way I’ve gone about it,” he added. “I don’t really look back and say ‘argh, I should have done that deal then and I shouldn’t have been this or that’, I’m pretty happy.

“If my career ended today, am I disappointed I don’t have a world title? Yes. But could have I actually done anything to change that over that 10 years? Probably not.

“But I’m not done, so we’re good.”

That change was expected to come in 2021 with Renault gearing much of its focus towards an overhaul to F1’s sporting, technical, and financial regulations, which it had long targeted as its best opportunity to make a competitive leap forward in its long-term ambition of returning to winning ways.

Last week’s postponement of the technical rules until 2022 means such a performance jump will no longer be possible, with teams now set to carry over their 2020 cars into 2021.

This delay could have huge ramifications on what Ricciardo decides to do next. He is desperate to be fighting for world titles, so would he really be willing to hang around for an additional year when competitive seats could free up elsewhere?

That is where Vettel comes into the equation.

Much like Ricciardo, Vettel is yet to find the success he would have hoped for when he departed Red Bull for Ferrari in 2015.

Entering his sixth season at the Scuderia, Vettel has amassed 14 victories in the famous scarlet red overalls but is yet to achieve his dream of emulating his hero Michael Schumacher in winning the world championship for F1’s most famous team.

Vettel heads into 2020 off the back of three frustrating seasons in which he has failed to topple the dominant juggernaut combination of Mercedes and Hamilton. The last two seasons have been particularly disappointing, with a flurry of mistakes marring his 2018 campaign before he saw his position as Ferrari’s number 1 come under threat last year.

Vettel won just once in 2019 and slumped to fifth in the championship - his worst result since his final season at Red Bull in 2014 - after being out-performed by the rising sensation that is Charles Leclerc. Tensions rose between the two over the course of their first season together as teammates at Ferrari, which came to a head in Brazil when they crashed into each other.

The German is also out of contract at the end of the season and heading into a “key moment” of his career, according to Ferrari team principal Mattia Binotto, who also said Vettel’s future at the team is “in his hands”.

Binotto has been insistent that Vettel is Ferrari’s obvious and leading candidate for a 2021 seat alongside Leclerc, adding that discussions between the team and driver have already begun.

As a four-time world champion, there is no doubt that Vettel has it within himself to recover from his recent disappointment and turn in a strong campaign, though Ferrari will be wary of how its drivers act towards each other in the heat of on-track battle this year.

What it needs now is a harmonious driver pairing in order to take the fight to Mercedes. If things escalate between Vettel and Leclerc into a full out civil war - much like the one that destroyed the Hamilton-Alonso partnership at McLaren - Ferrari will need to look elsewhere for a partner to Leclerc, who is clearly emerging as its future.

Ferrari have long been admirers of Ricciardo, who has been linked to Maranello in recent years. He would be an attractive option for Ferrari as a proven race-winner, while his marketable personality would come as an added bonus.

Ricciardo would prove a stern test for Leclerc and although he certainly wouldn’t settle for number two status, he is unlikely to throw his toys out of the pram and potentially destabilise the team. Even during his intense rivalry against Max Verstappen at Red Bull, these attributes were not present. In any scenario that saw Vettel leave Ferrari, Ricciardo must surely be its standout replacement option.

Speculation over a possible swap ramped up recently when Renault team boss Cyril Abiteboul refused to rule out Vettel as an option for 2021 if Ricciardo did decide to leave.

“I don't want to say no, as he is a great driver, and a great champion," Abiteboul replied when asked if the four-time champion was an option. ”We worked together on the engine side and we won together.”

Vettel would be a great capture for Renault, filling the team’s headline slot alongside Esteban Ocon and providing it with a natural leader. Vettel’s wealth of experience would also be a huge draw, particularly when it comes to set-up direction and car development.

Arguably, such a move would have bigger appeal to Renault than for Vettel, with a step down to the midfield ranks maybe not being a hugely attractive option for Vettel.

It would, however, take some of the spotlight away from him in a less-pressured environment, allowing him to fully embrace his love and passion of racing once more. And if Renault did get the 2022 technical rules right, Vettel could be onto a winner.

While there is much to be resolved between now and then in a season which doesn’t even have a confirmed start date yet, the idea of a Ricciardo-Vettel swap doesn’t seem so far-fetched…