Valentino Rossi led a MotoGP track session for the first time as a Ducati rider, during a damp morning warm-up session at Assen.
Spots of rain began falling as the 20-minute session began, and got steadily heavier.
Only ten riders set a 'proper' lap time, with Rossi - who will start just 11th on the grid - fastest on his third of six laps.
Yamaha's reigning world champion Jorge Lorenzo was 4.260sec slower than his former team-mate, although the lap times meant very little.
With Loris Capirossi injured in Friday qualifying, only 16 riders will start this afternoon's race, which could see the first flag-to-flag (bike-swap) race of the season should the off-on rain showers continue.