MotoGP icon Valentino Rossi left Michael Schumacher "stunned" by his lap times during his first Formula 1 test for Ferrari in 2004, according to a former engineer who worked with both drivers that day.

Nine-time world champion Rossi flirted with a move to F1 on a number of occasions, with his maiden test for Ferrari coming at Fiorano in 2004 when both he and Schumacher were at the height of their powers.

Rossi was given the chance to sample the Ferrari F2004 car around the Italian manufacturer's private track with suport from engineer Luigi Mazzola, who remembered the test on his Facebook page.

"I do not remember exactly how many tests we did with Valentino Rossi at Ferrari, certainly at least seven," Mazzola wrote.

"At the first, Valentino went on the track and did about 10 laps - and on the last, it was an incredible time.

"I remember that Michael Schumacher, who was with me looking at the telemetry, had a stunned looked, almost incredulous."

Rossi would go on to appear in many more F1 tests for Ferrari between 2004 and 2009, often matching the series' regular drivers.

The current Yamaha rider is reported to have held an option on a contract to race for Ferrari in 2007, only to opt to stay in MotoGP instead.

Mercedes extended an olive branch to Rossi to get back in F1 machinery last year when team boss Toto Wolff said the Italian was welcome to sample its car sometime, having given rival Jorge Lorenzo a private test back in 2016.