Melbourne: World No. 1 Rafael Nadal faces three weeks out after being diagnosed with a torn inner hip muscle during his Australian Open quarter-final defeat, his management said on Wednesday.

The 16-time Grand Slam champion had a scan in a Melbourne hospital after he retired early in the fifth set of his match with Croatia’s Marin Cilic on Tuesday.

“The MRI [scan] showed a grade one injury of his illiopsoas on his right leg,” his management said in a statement.

“He will be resting over the next days once back in Spain and will start with anti-inflammatory physiotherapy.

“He will start his rehabilitation and pre-adaptation process to the tennis court in two weeks, starting progressively his training and practice.”

The Nadal team said the Spanish star was expected to be fully recovered in three weeks and could resume playing in Acapulco late next month.

“Three weeks is the normal time to totally recover and he will resume his tennis schedule as planned, playing Acapulco, Indian Wells and Miami,” the statement said.

The Spaniard was forced to withdraw when trailing Marin Cilic 2-0 in the fifth set and called on tour organisers to do more to halt injuries to top players.

His comments followed the withdrawals of Andy Murray and Kei Nishikori before the tournament started and Novak Djokovic struggling ahead of his exit on Monday.

“Somebody who is running the tour should think a little bit about what’s going on. Too many people are getting injured,” Nadal said.

“I don’t know if they think a little bit about the health of the players. I don’t know if we keep playing on these very hard surfaces what’s going to happen in the future with our lives.”

It was the second time Nadal had been forced to pull out with injury in Melbourne after calling it quits in the third set of his 2010 quarter-final against Andy Murray with a knee problem.

Nishikori feels he needs more time to reach full fitness after going down 6-3, 3-6, 6-4 to American Dennis Novikov in the opening round of a Newport Beach ATP Challenger Tour event in his first match since undergoing right wrist injury in August.

The former US Open finalist, who last year reached the fourth round of the Australian Open in Melbourne, was forced to withdraw from the year’s first grand slam and chose the second-tier event in California to launch his comeback.

“I had expected it to be tough and it was,” Nishikori said.

“I’m not confident yet so I can’t hit aggressive shots. It’s going to take some time. I made mistakes where I shouldn’t have, and there are a lot of gaps I need to fill. There were both good and bad.”

Nishikori was ninth in the world rankings before suffering the injury ahead of the Cincinnati Masters last August.

Serena Williams, who has not played a competitive match since capturing last year’s Australian Open, will return to the court next month at a Fed Cup tie, the US Tennis Association has announced.

Williams was pregnant when she won her 23rd major crown last January in Melbourne. She gave birth to a girl, Alexis Olympia, last September and married father Alexis Ohanian in November.

The defending Fed Cup champion Americans will play host to the Netherlands in a first-round tie February 10-11 on an indoor hardcourt at Asheville, North Carolina.

Joining 22nd-ranked Williams on the US squad will be her sister seven-time Grand Slam champion, Venus, and ninth-ranked CoCo Vandeweghe, a semi-finalist at last year’s US and Australian Opens in her best major results.