Thursday's second free practice sessions at Assen have been cancelled for all three grand prix classes - MotoGP, Moto2 and 125 - due to a major oil spill.
The oil was dropped over large parts of the circuit by Alex Baldolini during this morning's (wet) first Moto2 practice.
Accidents caused by the oil forced that session to be red flag and, after a 30-minute delay for the 125cc class, it was announced that their FP2 session would be rescheduled.
The start of second MotoGP practice was then also delayed, and with oil still oozing from the asphalt the decision was eventually taken to cancel all of this afternoon's sessions.
This morning's first free practice sessions were mainly held in wet conditions.
Marco Simoncelli (Gresini) was fastest in the MotoGP class, followed by Valentino Rossi (Ducati), Casey Stoner (Repsol Honda), Andrea Dovizioso (Repsol Honda), Jorge Lorenzo (Yamaha) and Cal Crutchlow (Tech 3 Yamaha).
The Dutch TT is the only MotoGP race to be held on a Saturday.
UPDATE: An extra 45 minutes will now be added to Friday morning's final MotoGP practice session (extending it to 90-minutes).