"He told me that he doesn't look at all to be in shape. Beckham is super-ambitious," Arsene Wenger told reporters this week.
"If, in his mind, he wanted to play in the Premier League he would not have gone on holiday. He would have prepared and come in and tried to impress me. He told me he has done nothing at all."
Beckham admitted it might take "a few weeks" to get fully fit.
"It won't take long," he said.
He explained that he could not play for another club in England except Manchester United, where he won six Premier League titles and the Champions League before moving to Spain in 2003.
"It's the team I support and the team I dreamed of playing for," said Beckham, who to Manchester as a teenager and progressed through the club's academy.
"I'm very honored by the offers I had from other Premier League clubs but I didn't want to play there unless it was for Manchester United."