Sylvain Guintoli admitted he found it hard to adapt to from Superbike to MotoGP machinery, during Monday's Mugello test.
The Frenchman, who raced for Pramac full time in 2008 and now races a satellite Ducati in World Superbike, is set to return to the MotoGP paddock to replace the injured Loris Capirossi for the next two races.
Prior to the Mugello test, Guintoli hadn't ridden a Ducati MotoGP bike since 2008, with his most recent taste of premier-class power being at last year's Brno test, when he helped out at Rizla Suzuki.
Guintoli ride for a mammoth 87 laps, but his best lap time was five-seconds behind Casey Stoner and three-seconds behind Pramac regular Randy de Puniet.
"I had some difficulties today, especially adapting to the tyres. It was not easy to ride a MotoGP bike after such a long time," said Guintoli.
"But I'm learning and I think if I get the opportunity to ride at Sachsenring I'll be even more confident with the bike."
Capirossi was injured during qualifying for the Dutch TT. The German Grand Prix will be held at the Sachsenring on July 17, before which Guintoli will race in this weekend's Brno WSBK round.
Guintoli achieved a best finish of fourth as a full-time MotoGP rider.