MotoGP rookie Mika Kallio is a doubt for next weekend's US GP at Laguna Seca after crashing at Assen.

The Finn was just a few corners away from scoring a career best sixth place in the Dutch TT when he crashed at high speed and badly injured his left ring finger.

Kallio had just overtaken James Toseland to retake the lead of a thrilling six rider battle, but lost control of his Pramac Ducati through the fast turns at the end of the last lap.

When he fell, Kallio's left hand became trapped under his Desmosedici, burning away his glove and part of his finger.

"So painful, an incredible pain in the same finger I had already injured during my first MotoGP test in Valencia, maybe better to cut it off," he said.

"I will have to check the situation of my hand back in Finland, but I'll do whatever is possible to race in Laguna Seca."