Nico Rosberg has warned record-breaking multiple F1 world champion Michael Schumacher that it will not be easy for him if he does opt to come out of retirement and compete in F1 2010.

Rosberg will potentially team up with Schumacher next season, assuming he does join Mercedes GP - former 2009 F1 Constructors' champion, Brawn GP. However while there is still no official confirmation, rumours persist and Ferrari president Luca di Montezemolo recently revealed that the 40-year-old had told him there was 'a very, very, very strong possibility that he will drive for Mercedes' in 2010 [see separate story - click here].

Rosberg is not convinced though that his compatriot will be the same if he does comeback, especially as he has been out of the sport now since 2006.

"It will not be easy for him," the 24-year-old told German newspaper, Stuttgarter Zeitung.

"When you stay away from F1 for a long time, it takes time to get used to all the trial sessions again, it is not simple."

Rosberg meanwhile added that the main thing now though is for Mercedes to make a decision.

"I hope that my team-mate will be sorted out pretty soon and at the moment the rumours are very strong for Michael Schumacher," Rosberg added to BBC Sport Online.

"I have no idea if it is true or not but obviously if he would join that would be an absolutely fantastic move [for Mercedes and F1]."

If Schumacher doesn't return next year, Nick Heidfeld is believed to be the favourite to get the nod alongside Rosberg. Robert Kubica, who has a deal with Renault, is also believed to be a possibility.