The father of Australian tennis player Lleyton Hewitt has accused his son's critics of jealousy and defended his decision to accompany him on tour.

Glynn Hewitt told the Sydney Daily Telegraph on Friday that Lleyton had been unfairly criticised after his first-round loss at Wimbledon on Monday to Croatian Ivo Karlovic.

"It says a lot about the fickle nature and jealousy of some people," Hewitt Sr. said. "It's at times like these when you find out who your true friends are.

"To Lleyton, he's lost a tennis match -- an important match at an important tournament -- and it hurts him to lose.

"But, by the same token, this experience has enabled him to learn whose support he can appreciate and those who are fickle."

Hewitt Sr. said he was offended by claims from 1958 Wimbledon champion Ashley Cooper that the presence of him and his wife at Lleyton's matches was a distraction for the 22-year-old.

"How Ashley Cooper, who I've met once and Lleyton's met once, can make a comment about what family situation should be or should not be is beyond me," Hewitt Sr. said.

"We're on tour - and not as much as most people think - because Lleyton wants us here as his support. He is financially independent and mature enough not to have us here if that's what he chooses."