Reigning MotoGP champion Marc Marquez has ruled out the possibility of racing in two grand prix classes during the same season.

Competing in more than one championship used to be commonplace in motorcycle grand prix, with Freddie Spencer famously winning the 500cc and 250cc crowns in 1985.

Marquez broke Spencer's long standing record as the youngest premier-class race winner last year and the American was present for the recent presentation of Marquez's book - when the 21-year-old Spaniard remarked that it would be fun to race in two categories.

Marquez has won all six MotoGP races this season from pole position, while Dorna's Carmelo Ezpeleta is said to be willing to rearrange the race day schedule if Marquez wanted to take up the challenge.

But when asked further about his 'two class' comments at Catalunya on Thursday, Marquez was quick to stamp out the speculation:

"I said that it would be funny, but it is too difficult - or nearly impossible. Before was completely different. Now after practice or the race you have the data recording and everything that you need to work on in the pit box, also the press conferences.

"I think it is impossible to race into categories now. I don't have enough time. Of course it would be fun, but now -impossible!"

Marquez was a world champion in both the 125cc (now Moto3) and Moto2 classes before joining MotoGP with Repsol Honda last year.

Meanwhile, asked about the growing pressure to continue his unbeaten run in front of his home fans in Barcelona on Sunday, Marquez admitted:

"It looks like here if we don't get the victory it will be a disaster. And of course you can feel the pressure, but I know that it will not be a disaster to finish on the podium. The first target is to win the race but the second target is to finish on the podium.

"Okay if you don't finish on the podium, or you don't finish the race that can be a disaster. But anyway it will arrive someday at some race, maybe this one, where it will be impossible to win."

Marquez finished a close third behind countrymen Jorge Lorenzo and Dani Pedrosa at Catalunya last year and he considers it one of his tougher events - although notably not at tough as Mugello, when he won last time.

"I love the layout of this track but the biggest problem for me are the kerbs," Marquez revealed. "Inside the kerbs are really, really high and so to put the elbow is so difficult.

"There is not enough space to put the shoulder, the knee and everything. It is so difficult to use all the track but it is the same for everybody so we must manage that.

"I think Pol [Espargaro] also has some problems with that! This year more riders will have the same problem because everybody uses that [elbow down] riding style.

"But overall for me Mugello is a little bit more difficult than Catalunya. Here the track is bigger, you can use more than one line. In Mugello you need to be more precise."

Marquez's perfect season has allowed him to build a 53 point title lead, more than two race wins, after six of 18 rounds.