Dani Pedrosa says he is unlikely to return from injury in time for Saturday's Dutch MotoGP at Assen.
The Spaniard has missed the last two races after breaking his collarbone in a crash with Marco Simoncelli at the French Grand Prix in May.
"It will be very difficult for me to make Assen, but I really believe I will be okay for Mugello (1-3 July)," said the Repsol-Honda rider.
"I want to return as soon as possible, but I want to do the right thing."
Britain's Cal Crutchlow is also a major doubt for Assen, following a successful operation on his broken left collarbone.
He was forced to miss his home race at Silverstone after picking up the injury in a crash in qualifying.
His Tech 3 Yamaha team-mate, Colin Edwards, finished third in that race, just a week after a similar fracture.
"I don't know if I will ride but I'll be trying 100% to be there if I can," said Crutchlow.
The 25-year-old crashed his Yamaha early on in the qualifying session at Silverstone and was transferred to Oxford hospital, suffering the break and concussion.
His collarbone was broken in five places and he has had a titanium plate inserted.
Doctors were also concerned that he may have fractured his neck but CAT scans showed no damage.
"The operation on my collarbone was a success and the doctors seem really happy with the outcome," said the Coventry-born rider.
"But I am still in a lot of pain. Unfortunately, the break is a lot worse than the one Colin Edwards had in Catalunya and I've got different pain and movement levels.
"I've spent two days lying on my back with a suspected neck injury, so my shoulder is swollen."