"I missed everything - the tournaments, the fans, the stadiums, the other players, I really missed everything," he said.
"But now I'm here again and I'm trying to play a good level. Everything was difficult after my surgery, but those bad things are the past. Now I am having a good 'present', I'm healthy, and if I work and still improve my game, I will have a good future."
Wimbledon is the most important tournament of the year for me
Novak Djokovic
Del Potro lost to Nadal on his only previous appearance at Queen's Club in 2007 and is determined to improve on grass.
"I like London, I played at the Aegon Championships a couple of years ago and I really enjoyed it," said Del Potro.
"If you want to be a really good player you have to win on grass courts. I never had good results on grass before so this year could be a chance for me to improve my game on grass at Queen's and at Wimbledon.
"I have to learn many things on that surface but I will be ready to do it. Any tournament I play I want to win and If I can play my best level I think I can do it."
Roddick won the title at Queen's Club in 2003,2004,2005 and 2007, putting him alongside John McEnroe, Boris Becker, Lleyton Hewitt, Roy Emerson, MJG Ritchie and AF Wilding as the only four-time winners.
"Over the years I've had a lot of success at The Queen's Club. It has real tradition and I love the whole month in London," said the American.
"Queen's has the best grass courts in the world - they play perfectly and so the Aegon Championships is a great way to prepare for Wimbledon."
Djokovic has made winning a first Wimbledon title his priority for 2011 after landing his second Grand Slam at the Australian Open in January.
"Wimbledon is the most important tournament of the year for me," said the two-time All England Club semi-finalist.
The Serbian will be joined at Queen's Club by Nadal, raising the possibility of a repeat of their 2008 final.
"The Queen's Club has got great grass courts, it's a great atmosphere with always a packed house of spectators and you just feel good there," said Djokovic.
"Rafa and I had an incredible match in the Queen's final in 2008 and it was the closest I ever got to a grass-court title. I really want to do well at Queen's and at Wimbledon this year."
Nadal beat Djokovic 7-6 7-5 in the 2008 final before going on to win his first Wimbledon title three weeks later.
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