Movistar Yamaha rider Valentino Rossi has admitted that it will be tough to stay atop the MotoGP standings for the second half of the season as faces stiff competition from Marc Marquez and Jorge Lorenzo.
Marquez, who is the reigning MotoGP champion, has endured a turbulent season thus far which sees him occupy fourth place on the standings, trailing Rossi by 65 points.
Lorenzo too made a poor start to the season, but righted the ship with four race wins in a row to cut Rossi's lead down to one point in June before the Italian consolidated his lead and extended it to 13 points after triumphing at Assen and coming third at the German Grand Prix.
With the MotoGP season set to resume this weekend in Indianapolis, Rossi conceded that he will have to be at his best if he wants to maintain top spot in the standings and win his seventh MotoGP title.
"It's difficult this year because we are not just two riders but three, and also Iannone," Rossi told reporters. "It's a great season because a lot of riders are very fast and the level is so high.
"You have to concentrate all weekend, it's important because if you make mistakes during practice you can lose a lot of points. All the top riders have great experience and don't have any weak points. Nobody has bad tracks.
"Jorge and Marc are very strong at all the tracks so you need to take points to the end of the season. I worked a lot on qualifying because sometimes I was not strong enough."
Rossi also feels that it would be a grave mistake to rule Marquez out of the title race, as the Repsol Honda rider showed signs of recovery after finishing second at Assen and first last time out in Germany.
"At the beginning of the season he had some problems with the feeling with the bike and he lost some points," Rossi said. "But he has come back strong. The distance is quite a lot in the points but we are only in the middle of the season so we have to keep concentrating."