Brisbane - Rafael Nadal on Wednesday withdrew from the season-opening Brisbane International after an MRI revealed a slight strain of his left thigh.
Nadal, who had a first round bye, was scheduled to play his second round match against Frenchman Jo-Wilfried Tsonga on Thursday.
However, after conferring with his doctors he decided to withdraw to ensure he would be fit to play the Australian Open later this month.
Nadal, the current world No 2, has not played a main tour event since a knee problem forced him to retire during his US Open semi-final against Juan Martin del Potro in September.
The 32-year-old had surgery on his ankle in November to remove a loose intra-articular body and only resumed training three weeks ago.
He played the opening round at an exhibition event in Abu Dhabi last week, where he lost to South African Kevin Anderson.
"I feel good, but after a long period of time without competing, I felt the leg tightening a little bit in Abu Dhabi in the first match," he said.
"That's why I didn't play the second (match). So I came here. I did an MRI, and it shows a very small strain on the left thigh, but it's there."
Nadal said doctors were confident he would be fit to play in Melbourne.
"They say that it's a very small thing, but it can become a big thing, because a strain in the muscle is dangerous," he said.
"When you increase the intensity on the muscle when competing, then there is a big risk to make it something bigger.
"Today it's not big. I feel better than four days ago. Probably I'm 100 percent in five days. And then I have plenty of time to prepare for Melbourne."
of matches played at the ATP/WTA Brisbane International tennis
tournament at the Queensland Tennis Centre on Wednesday (X denotes
Yasutaka Uchiyama (JPN) bt Kyle Edmund (GBR X3) 7-6 (8/6), 6-4
Grigor Dimitrov (BUL X6) bt John Millman (AUS) 6-3, 6-4
Kei Nishikori (JPN X2) bt Denis Kudla (USA) 7-5, 6-2
Milos Raonic (CAN X5) bt Miomir Kecmanovic (SRB) 6-3, 7-6 (7/2)
Jeremy Chardy (FRA) bt Nick Kyrgios (AUS X8) 6-7 (5/7), 6-2, 6-3
Anastasija Sevastova (LAT X8) bt Harriet Dart (GBR) 6-2, 6-0
Anett Kontaveit (EST) bt Petra Kvitova (CZE X4) 7-5, 7-6 (7/1)
Karolina Pliskova (CZE X5) bt Marie Bouzkova (CZE) 7-5, 6-2
Donna Vekic (CRO) bt Kiki Bertens (NED X6) 7-6 (7/5), 1-6, 7-5
Ajla Tomljanovic (AUS) bt Johanna Konta (GBR) 6-2, 7-6 (7/2)