Stepanek said he was diagnosed with a muscle tear after Tuesday's win over John Isner of the United States, and was in pain Wednesday morning after hitting practice shots.
The Czech player had been due to play Vincent Spadea of the United States at the Wimbledon warmup tournament.
"It's not a great moment for this to happen because I feel I've been playing really well and trying to get back to the top 10 and now I'm scared if I'm going to be playing Wimbledon,'' the 15th-ranked Stepanek said.
Stepanek is seeded 16th at Wimbledon, which starts Monday.
His withdrawal at Nottingham comes a day after sixth-seeded Dmitry Tursunov of Russia was kicked out for storming off the court during a doubles match after disputing a line call. Tursunov and Chris Haggard of South Africa were trailing 6-4, 3-1 to Italian pair Simone Bolelli and Andreas Seppi in Tuesday's match. ATP rules state that no player can leave the court without the umpire's consent.
"After reviewing the situation, the ATP supervisor has withdrawn Dmitry Tursunov from the singles tournament,'' the ATP said in a statement.
Tursunov had been set to play Thomas Johansson of Sweden in the second round.
Stepanek advances at Nottingham
EURO TOUR COULD TAKE THE MICK
WOODS OPTS FOR OPEN RETURN
