MADRID – Rafael Nadal is hopeful the knee injury that forced him out of the Australian Open will have healed in a week or less, the world number two said on Thursday.

"I am not worried," Nadal told reporters at Barcelona airport before heading to a clinic for tests overseen by Spanish tennis federation (RFET) doctor Angel Ruiz Cotorro.

"I just have a little tweak and I hope to have recovered in a week or even less," he added.

The injury forced the 23-year-old defending champion to retire from his quarter-final at Melbourne Park against Andy Murray on Tuesday.

The Briton had already won the first two sets before Nadal called for a medical time out and he lasted just a few more minutes before he told Murray he could not continue.

Nadal said it was a recurrence of the problem that forced him out of the defense of his Wimbledon title and away from the ATP Tour last year for around two months.