Former Australian greats have defended Bernard Tomic's retirement one set into his opening round Australian Open match against world No. 1 Rafael Nadal, despite an initially hostile reaction from a disappointed, perhaps sceptical, Rod Laver Arena crowd.

Tomic, who said he first felt the groin injury during a practice session on Monday, had been taking medication before the match, but called the trainer after just three games, and was jeered by spectators when he declared himself unable to continue at the end of an opening set he lost 6-4 in 41 minutes.

"They've said it's going to be about seven days for the problem to heal itself, so he's the only one that can be the judge of that, and if there's an injury there he was probably going to do himself more harm by keeping on playing," said seven-time grand slam champion John Newcombe.

"It's a very difficult moment to pull out of the match like that, and I can't imagine him pulling out unless there was something wrong and it was hindering him, and you get afraid you're going to do yourself more harm. It's only the beginning of the year, there's a big year ahead and he did what he thought was best for himself. People have to think what they think.

"I just hope that this year, 2014, he keeps himself 100 per cent fit for all of the year, and does himself justice, because it's pretty obvious, isn't it, that he got down to 27 in the world, and now he's languishing around the 50s. When he's fit and playing to his full potential, he can be a top 20 player, so he needs to do that for 12 months of the year and prove to himself he can do it."

Former Wimbledon semi-finalist Jason Stoltenberg, now coaching rising women's star Ashleigh Barty, said Tomic's discomfort appeared genuine.

"Unless he's a really good actor, his leg looked like it was hurting too much," Stoltenberg said.

"So it appeared like he was hurt and he had a potential three hours ahead of him against Rafa, and probably did the math and figured out that he was in deep trouble. Playing against Rafa when you're fully fit is a daunting prospect. But at the end of the day only he knows what he was feeling. It's hard to speculate.

"I can't see any reason why Bernie wouldn't want to play that match. It's a tough draw, but someone's gotta play these guys, and until he gets himself in a position where he's seeded, it's always gonna happen. I can't think of any reason why he wouldn't want to give it everything he's got."

Stoltenberg said Tomic may have been judged on his history, which has included several allegations of tanking, including against Andy Roddick at the 2012 US Open. "That's just natural," he said.

"Everyone knows, everyone talks about it, so when he has a legitimate injury, people are gonna question it now. It is what it is. He'll just have to deal with that. It's a reaction to his past actions."

Another former top 20 singles player and doubles star, Mark Woodforde, sympathised with the often-maligned 21-year-old. "To beat the best you have to feel 100 per cent yourself. He was managing well but managing isn't enough against Rafa," said Woodforde, the coach of Marinko Matosevic.

"I don't think there's anyone more disappointed then Bernard. I think the crowd reaction was because there was such a build-up and they were missing out on a good match. I don't think they were coming down on him. They had to wait so long for them to get out on centre court then it was cut short. I never felt it was towards him.

"What was the point of staying out there if he couldn't give 100 per cent? How does he conjure up a win when he's not 100 per cent? Some might have played on but there would have been some who stopped before the set.

"He was in pretty good form last week and I saw him practice here in December. I know the hours he put in and (he was) working so well. There was such a good feeling heading into the summer. Unfortunately he couldn't continue."

Tomic was scheduled to appear at a news conference at Melbourne Park on Wednesday afternoon.