Aprilia opened its 2021 MotoGP track activities with a three-day private test at Jerez, where Aleix Espargaro and Lorenzo Savadori continued development work on the revised RS-GP.

While Espargaro cautioned that engine power is still lacking, he felt there have been "interesting improvements" in several other areas.

"The base of the 2021 RS-GP is definitely promising, it's only the first tests but the times were good on a track that is not historically the best for us," said the Spaniard.

"There is still a lot of work to do, especially on the power side, but in terms of ergonomics, chassis and electronics there have been some interesting improvements.

"Now we are waiting for Qatar, where we will be together with all the other riders and we will understand our real level. With the hope that Fausto [Gresini] will soon be back on track with us."

Updates made to the bike for 2021 include a new chassis, new carbon-fibre swingarm and new engine.

Espargaro's team-mate is yet to be confirmed but Savadori now looks the clear favourite, underlined by his presence at the test, although Bradley Smith's manager says they are still in negotiations with Aprilia.

"First of all my thoughts go to Fausto, who is currently fighting a tough battle. I know his spirit and his determination and we miss him very much!" Savadori said of team boss Gresini, who has been in intensive care with Covid-related respiratory problems since late December.

"It's great to be back on track after the break, it's always a special moment. Unfortunately these tests have been conditioned by a problem with my right shoulder that has prevented me from being 100% fit.

"In any case the feeling with the 2021 bike was good at first impact, it seems to have improved from all points of view even though I think we still need to work on it.

"My goal is to be in perfect shape for the next test in Qatar."

Aprilia is the only remaining factory that can use its race riders for private testing, as part of the MotoGP Concessions package.

The first official MotoGP test of the season will be held in Qatar on March 5-7.