Federer hopes to recover from groin problem after lucky escape

After pulling off a miracle victory against American world number 100 Tennys Sandgren by saving seven match points, Roger Federer remained optimistic about recovering fully from a groin problem in time for Thursday's Australian Open semi-final.

The Swiss third seed scripted a nerve-wracking 6-3, 2-6, 2-6, 7-6(8), 6-3 comeback victory on Rod Laver Arena on Tuesday to continue his bid for a record-equalling seventh title at the Melbourne Park.

Federer called the trainer to the court during the third set against Sandgren and then took a lengthy medical timeout that he later said was for a problem with his groin.

His movement was visibly impaired for the rest of the match but that did not stop the 38-year-old from reaching a record-extending 15th semi-final at the Australian Open.

Next up for the 20-time Grand Slam winner will be Novak Djokovic, who last year beat Rafael Nadal in the final to claim a seventh title at the Melbourne major.

"I don't know if you can call it an injury. It's just pain and problems. I need to figure it out now," he said. "But as it's not like in 18 hours, like you got a third round to play, semi-finals, you have an extra day, adrenaline, there's a lot of things. Two good nights of sleep, doctors, physios."

"Hopefully we'll find out that it's actually nothing bad, that it was just the groin that went really tight from playing a lot, who knows what, from nerves. I don't know. I'm hopeful."

Just prior to the medical timeout, Federer was warned for obscene language - something that is rare for the Swiss - after a complaint from a line judge.

He first confronted the line judge before getting involved in an argument with Serbian chair umpire Marijana Veljovic. Federer said he found the warning 'bit tough' but accepted it.

Asked if the language was not English, Federer said with a smile: "It was a mix. Clearly she speaks mixed. Didn't know that (smiling). Next time I got to check the lines-people."

While Federer did not feel as physically exhausted as he did against John Millman, when he won six straight points from 8-4 down in the final set tiebreaker to stay alive, Sandgren had nothing left in the tank - both physically and emotionally.

If watching match points slip by was not hurtful enough for Sandgren, he also had to deal with some physical pain when a ball girl accidentally ran her knee into his calf during changeover in the fourth-set tiebreak.

"That was physically painful. She was apologetic and everything. Accidents happen, so that wasn't a big deal," he said. "It stung a little bit at the time. It didn't bother me when the point started, no."