Valentino Rossi out to extend lead in Catalunya

Valentino Rossi is hoping to extend his championship lead as Yamaha team-mate Jorge Lorenzo looks to continue his strong run of form as the MotoGP moves to Catalunya.

Rossi won the first three races of the season, but wins for Lorenzo in Spain, France and Italy have closed the gap to just six points in standings heading into Sunday's Catalan Grand Prix.

Marc Marquez took out last year's GP, but has struggled for pace this year, something that has surprised two-time championship winner Casey Stoner.

"I did not expect to see Marquez still so troubled," Stoner said.When asked who the best rider in the field was, Stoner said although Rossi "leads the standings", Marquez has had "two great seasons."

"No doubt this is a good season, you never know who will win on Sunday Stoner added.

Marquez has found it difficult aboard Honda this season, but has form in his home GP, after finishing on the podium in 2013 and 2014.

After failing to crack the top 10 in qualifying, Marquez fought through the field only to crash out at the Italian GP last time out.

Rossi is yet to miss out on a top-three finish in 2015, but has struggled to match his team-mate's qualifying pace this year, something he will need to fix if he is to stand atop the podium again.

Lorenzo is on the record as saying it will be difficult to topple Rossi in the championship race, despite closing the gap his team-mate had opened up at the start of the season.

"It was a different situation when I was 29 points behind than now when it's down to six, but even like that it's difficult to close in on Valentino on points because he is always on the podium," Lorenzo told the official MotoGP site.