LONDON — Roger Federer reluctantly agreed Thursday that he is the favorite to win the gold medal in mens singles. But he was the favorite in 2004 and 08, too.Federer was upset by Czech teenager Tomas Berdych in the second round in Athens, and American James Blake got his first victory ever over Federer in the quarterfinals at the Beijing Games.The pressure is always big because it is a different type of event that only happens every four years, Federer said Thursday. Thats not something were quite used to, knowing you only have maybe one, two, three or four chances in your life. On the tennis tour, you take it one by one, and it just keeps on coming, another highlight after another.... I already have an Olympic gold. I know its maybe the doubles, not the singles, but nevertheless nobody can take that away from me and Stan [Wawrinka]. So I go into it with great excitement and a lot of motivation to do well.Federer, 30, will not have to worry about defending Olympic champion Rafael Nadal, who pulled out of the Games citing conditioning issues because of recurring knee problems.It was a big surprise to see Rafa out of the Olympic Games, being he was defending champion, Federer said. It was a big blow for the Olympic Games, but he must have his reasons. I dont know if it was his knee or just his preparation wasnt good enough, but obviously its exciting for the rest of the field regardless if Rafa is here or not.Federer returns to the All England Club on Saturday, where earlier this month he won a record-tying seventh Wimbledon title. He is ranked first in the world and has won 17 grand slams, so an Olympic gold medal in singles would be icing on his trophy case.What probably makes [the Olympics] a tiny bit tougher is in Wimbledon we play seven matches, best-of-five sets; here, we have play five matches, best-of-three, and then only the finals best of five, Federer said. That puts margins closer to each other, I believe. If it would have been best of three in Wimbledon, I would have lost third round. ... It just goes to show a bad five minutes or a bad couple of points could cost you a tournament. Im aware of that, but I do believe winning Wimbledon three weeks ago is going to help me with my confidence and my game to really do well here.