David Coulthard has warned the new breed of F1 stars like Lewis Hamilton and Sebastian Vettel to be prepared for Michael Schumacher to mark his return to top flight competition in 2010 in characteristically 'ruthless' fashion - suggesting they will be more surprised by his level aggression than he will by their turn of speed.

Schumacher's comeback this season with Mercedes Grand Prix has divided opinion, with some opining that the record-breaking seven-time F1 World Champion will simply be able to seamlessly pick up from where he left off more than 50 races ago at the end of 2006, as he chases an incredible eighth drivers' crown.

Others, however, contend that the combined effects of three years out of the cockpit, his motorcycling-induced neck injury from last February and - at 41 now - his advancing years will count against him, particularly with the top seats now occupied by the likes of Hamilton, Vettel, fellow world champions Fernando Alonso and Jenson Button, ex-Ferrari team-mate Felipe Massa, 2009 breakthrough performer Mark Webber and highly-rated young compatriot Nico Rosberg.

Whilst acknowledging that 'none of us can hold back time' and that the 91-time grand prix-winner is going to have a fight on his hands to hold his own against adversaries who are now closer to half his age, Coulthard - a man who raced wheel-to-wheel with Schumacher on a number of occasions during his own F1 career, and as such is well aware of just how aggressive the German can be - revealed that in a no-holds barred duel, he knows who he would still put his money on every single time.

"I am surprised that Michael Schumacher is back," the Scot confessed. "He has been out of F1 for three years, and off doing motorbikes and all sorts of other things. For the winningest driver in history to make a comeback at 41 and try to relive his youth by signing a three-year contract is tremendously exciting for motorsport in general. He is a great champion from a generation ago, and now he is coming back to mix it with all these young guys in their twenties.

"However tough people think racing has been in the past, there is nothing quite like trying to argue over the apex with Michael Schumacher. He defined a whole new era of motor racing, and I'm curious to know if he will be as impressive and ultimately as quick as he was. Michael is an incredible champion in F1, and I would be surprised if he was surprised about how difficult it is now. I think it will be more the other way round; I think the younger generation will be surprised by just how ruthless Michael Schumacher will be to achieve his goals.

"Does he still have that killer instinct that made him the great champion he was before? None of us can hold back time, and at 41, physically he cannot be as strong and sharp and fit as he used to be - but his intuitive ability to hang the car out on the limit will still be there."

One regulation change that could well play into Schumacher's hands in 2010 - indeed, the key regulation change of the off-season - is the ban on refuelling. Only the Kerpen native and long-time former Ferrari back-up Rubens Barrichello have experience of competing in F1 without fuel stops, given that such a scenario last featured in the sport back in 1993 - and Coulthard believes its renewed abolition will really help to separate the wheat from the chaff once more.

"[Schumacher] also has a lot of experience of having to drive a heavy car from his sportscar days with Mercedes," the 13-time grand prix-winner turned BBC F1 pundit mused. "I personally feel the real test of a driver is to race without refuelling. It's something we've not seen for many years, meaning a lot of the strategy has been decided by software and analysts telling the driver 'you must pit now, otherwise you will lose half a second'. The driver will be a much bigger part of the process now."