Roger Federer has withdrawn from the Stockholm Open after announcing that he is to take a break from the sport.

The world No 2, who was diagnosed with glandular fever in January, said he was unsure if he would play again before the end of the year but added that he needed a rest if he was to remain at the top of the game in the coming years.

"2008 has been a tough year for me as I was always playing catch up after being diagnosed with mononucleosis at the beginning of the year," he said.

"I feel fortunate to be healthy again, but I want to remain at the top of the game for many more years to come and go after the number one ranking again. In order to do that, I need to get a proper rest and get strong again so that I am 100 per cent fit for the remainder of the year or next year."

"At this point, I am not sure when I will be ready to play again, but I hope to be back at some point before the end of the year," Federer said.

Federer won his 13th Grand Slam title last month, taking his fifth consecutive US Open title after a difficult year in which he has lost finals at Wimbledon and French Open and lost his No 1 ranking to Rafael Nadal. His participation in the Madrid Masters later this month is in serious doubt as his entry to the Swiss Indoors in Basel. He had also been due to play in the Paris Masters and the season-ending Tennis Masters Cup in Shanghai.