Being booed and jeered by the crowd after withdrawing from his Australian Open match against Rafa Nadal was 'pretty unfair', Bernard Tomic said on Wednesday, adding he could have faced a four month injury absence had he continued playing.

The 21-year-old Australian, who has been criticized in the past for "tanking" - or deliberately not playing to his full ability during matches - withdrew from his highly anticipated first round clash with top seed Nadal on Tuesday with a groin injury after he lost the first set 6-4.

Tomic, who had appeared uncomfortable from the outset under the lights at Rod Laver Arena, was booed for his decision to call it quits even though he had raised his hand and mouthed 'sorry' to the packed center court.

"I felt like I got booed a little bit on court, which was pretty unfair," Tomic told reporters on Wednesday. "I think I was misunderstood.

"Obviously they thought I was shaking Rafa's hand because he's too good and I'm forfeiting the match because I can't play against him.

"So I needed to say it was my leg. I don't think they quite understood that it was my leg."

Tomic said scans on Wednesday had revealed a torn groin tendon that would keep him out for up to three weeks.

Medical advice suggested had he continued against the world number one on Tuesday he could have faced up to four months on the sideline.

"It's just a small one (tear). It's not that big," he said.

"But if I had played on it it would have been 10 times worse, they say, so I could have been out potentially for three, four months.

"Lucky I stopped in the end, because I would have done myself a lot worse playing with Rafa another few hours on court.

"Who knows? Could have been another few months more, and then I would have dug myself a deeper hole.

"I'm very happy I stopped. It was the right call."

Tomic's decision on Tuesday came shortly after local veteran Lleyton Hewitt had lost to Italian 24th seed Andreas Seppi in yet another marathon five-set match.

The world number 57 said he could understand why some of the fans had booed him after watching the 32-year-old Hewitt, renowned for hard fought five sets matches in his career, battle to the end while he withdrew after 39 minutes.

"I was watching the Lleyton match. It was very, very good tennis and amazing for Lleyton to come back and then having to play my match following, you know, a lot of people following.

"A lot of people showed up last night expecting a very good match. A lot of people paid their tickets.

"It's disappointing for that to happen. The form I was in, I was ready to challenge Rafa."