Bernard Tomic has described his inability to finish his first-round clash against Rafael Nadal at the Australian Open as "unfortunate".

The 21-year-old was forced to retire from the match with a groin injury after Nadal secured the first set 6-4 in Melbourne on Tuesday.

"It's unfortunate," the tournament's official Twitter page quotes Tomic as saying. "This opportunity I had playing Rafa was huge for me. Unfortunately I couldn't compete."

"I thought 'am I really going to spend a few more hours out on court hurting my body', and I felt sorry for the crowd and for me. He's a great champion, an amazing player. I wish I could have played him."

Nadal has joined Novak Djokovic, Andy Murray and Roger Federer in the next round of the tournament.