Belgrade: Tennis world number one Novak Djokovic said on Wednesday he was not certain he would be able to play for Serbia in 2012 Davis Cup due to his "packed agenda," Beta news agency reported.

Djokovic has already said he would skip the first round of the Davis Cup match with Sweden to be played in southern Serbian town Nis on 10-12 February in order to get some rest from the busy season.

"I am sorry that I will not play against Sweden in Nis... I can not promise that I will take part in this competition this year," Beta quoted Djokovic as saying.

Djokovic returned to Serbia, where he is considered a national hero, after winning the Australian Open in the longest finals in the history of this tournament against Rafael Nadal.

He recently said his main focus this year would be on the Olympic Games and the French Open, a Grand Slam win that would see him hold all four major titles at once.

Djokovic said his participation in the Serbia Open tournament -- which he won in 2011 -- this spring was not "definitive yet."

"I am on the list (of the participants), but it will be difficult to organise everything. In order to take part in it, I would have to make radical changes in my agenda," Djokovic said, adding that he would consult with his team.