Nadal also withdrew from a match in Abu Dhabi last week against Karen Khachonov.
"I tried to play and I wanted to play, but there were recommendations from the doctors", he said.
'I feel better than I did four days ago... "I need to try and find a way of working out how to get around some of the things I struggle with a little bit now". "But my main goal is to stay healthy, stay happy and try to play as long as possible".
Speaking at a press conference, he said: "I did an MRI and it shows a small strain on my left thigh".
Speaking about his chances at the Australian Open, the 2009 champion stated "my hope is to win the Australian Open and being honest, I feel myself playing well".
On hard courts, Nadal has finished just one of his last 13 hard court tournaments, finishing (and winning) only the Canadian Open.
"I had a good off season, as I said before".
The 17-time Grand Slam champion hasn't played a competitive match since September but said Wednesday he is working hard in practice and remains confident he will be ready to compete at the Australian Open, which starts January 14 at Melbourne Park.
"I won five events out of nine that I played", he said.
He had already been out of the sport for months trying to heal knee and ankle injuries, now a thigh has added to his list of concerns.
"And was awful news for me that things were not the way that I planned, but coming back from a period of time outside of the competition and coming back from surgery, you know, there's always a chance that this kind of stuff happens".
Nadal, who had a first-round bye, was scheduled to play his second round match against Frenchman Jo-Wilfried Tsonga on Thursday.
Cathay Pacific to honour cheap business-class tickets sold in error
The airline did not give any details on how the mistake happened or how many tickets were sold when the discounts were up. Seekingalpha.com has article titled " Cathay Pacific Airways (CPCAF) Investor Presentation - Slideshow - Seeking Alpha".