MotoGP title leader Valentino Rossi began the Indianapolis weekend on the back foot, being just tenth fastest in Friday practice.

The Movistar Yamaha rider was 0.672s behind team-mate and title rival Jorge Lorenzo, who narrowly led both sessions from Honda's Marc Marquez.

"It was a difficult Friday, because I wasn't strong or fast enough, already starting from this morning," said Rossi, who dropped as low as 14th in the afternoon session before switching from the hard to medium rear tyre to move into tenth.

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"We waited for the afternoon because usually the first practice at this track, the track is quite dirty, so we think the situation can improve. But in reality, this afternoon I was also worse. I was quite slow. At the end, I tried the new tyre, but I don't have the right balance and the right settings.

"I suffered very much, especially in braking. I don't have a front feeling for stopping the bike and I lost a lot of time. And also the change of direction with this track, you have quite a lot of change in direction. I'm too slow. The bike feels heavy, lazy, and I'm always in a delay for the next corner. I'm not good.

"Like I said, it was a difficult day. We tried the [medium] tyre at the end and it was a little bit faster, but not enough. The situation is also worse because Marquez and especially Jorge are very strong. They are very, very fast."

The Italian will need to at least defend his tenth place in Saturday morning's FP3 session to ensure direct access to Qualifying 2.

"We need to check the data and improve because already tomorrow morning is an important practice. We have to stay in front for the qualifying in the afternoon, but especially try to make a step because I'm quite slow," he warned.

Rossi is 13-points ahead of Lorenzo as the second half of the season begins this weekend.