Valentino Rossi and Maverick Vinales expressed surprise and bafflement at a sudden and unexplained drop in pace on the final day of MotoGP testing at Sepang.

The two had topped Monday's timesheets with 1'59.390 and 1'59.355 lap respectively but with the same tyres, bikes and track temperatures on Tuesday, the pace was significantly off. Rossi stuck in one lap of 1'59.449 but Vinales was a second slower than his team-mate and 1.717s off a new lap record set by Jorge Lorenzo.

"Today has been very difficult, I don't know why we lost many things. Especially in the afternoon. In the morning it was quite well. But anyway, we worked hard, we were trying to improve, so now we have to check the data and see what we can improve in Buriram," said Vinales at the track.

Rossi added: "We are a little bit worried, we need to understand why, because in the Valencia Test after the last race it happened exactly the same.Today it happened a little bit the same, so we need to understand why.

"We were struggling a little bit more from the morning with the grip. It was a bit more difficult to ride the bike at the limit. I was optimistic to improve the lap time. But was it impossible."