Yamaha test rider Wataru Yoshikawa has completed many miles on the YZR-M1, but the 41-year-old Japanese found Valentino Rossi's race machine 'quite different' to those he had previously ridden.
Yoshikawa is replacing nine time world champion Rossi at Fiat Yamaha from this weekend in Catalunya until the injured Italian is fit to return from a broken leg.
Riding on an unfamiliar track, Yoshikawa finished Friday practice in Barcelona 17th and last, with a best lap time 4.756sec slower than the sister machine of title leader Jorge Lorenzo.
However, Yoshikawa was only 0.258sec behind Honda test rider Kousuke Akiyoshi, who is substituting for the injured Hiroshi Aoyama and has a one race head start, having ridden in the previous Assen round.
Yoshikawa's only previous MotoGP race experience is a twelfth place as a wild-card in 2002.
"I have already ridden many laps on the M1 but this bike of Valentino's feels quite different to the test bike and I need some more time to become used to it,” said Wataru, whose feedback was given to crew chief Jerry Burgess via a translator.
“Today was quite tough because in this heat the track was quite slippery, which didn't make it so easy for me to learn it, but I felt better by the end. We need to do some more laps and I will be ready to improve tomorrow."
"It will be interesting now to see how much we can improve during the weekend, as he becomes more comfortable on the bike,” said team manager Davide Brivio.
Yoshikawa was three seconds behind the slowest full time MotoGP rider on Friday, rookie Hector Barbera.