Spanish tennis star Rafael Nadal, who has been sidelined with a knee injury since last summer, said he was pulling out of this week's exhibition tournament in Abu Dhabi due to a stomach infection.

Nadal, who planned to return to action on Friday, revealed his latest setback in a Twitter posting.

"I am really sorry to not be able to compete in Abu Dhabi this year. Everything was ready and I really want to return to competition, but the doctors have prohibited me from playing in Abu Dhabi because of a stomach infection that has given me a fever," Nadal said.

The 11-time Grand Slam champion began the summer on a high note by capturing a record 7th French Open title with a victory over world No. 1 Novak Djokovic of Serbia in the final, but he has not played since a shocking second-round loss at Wimbledon.

"In Abu Dhabi, they have always treated me really well and this is the first time that I will not be able to compete in this tournament. My recovery has gone well, my knees are better and, like I said, I really wanted to return to competition. I feel bad for my fans in the Emirates and around the world. I hope to be there next year," Nadal said.

Nadal told Efe in August that he was suffering from a knee ailment known as Hoffa's syndrome, which is also known as fat pad impingement and involves pain and swelling around the bottom and under the kneecap.

The Spaniard, known for his physically demanding style of play and incredible defensive skills, has struggled to stay healthy during his career, having been forced to withdraw from each of the four Grand Slam events due to various injuries.

Nadal announced earlier this month that he would play in the Barcelona Open, which will take place April 20-28, 2013, in the northeastern Spanish city. EFE