It is the inherent nature of the injury that has prolonged Sachin Tendulkar's [Images] comeback to cricket after undergoing surgery for a tennis elbow problem, sports injury specialist Dr Anant Joshi told rediff.com on Wednesday.

The Indian batting ace on Wednesday pulled out of the two-Test series in Zimbabwe, commencing September 13. He was selected to the Test team subject to regaining full fitness.

Dr Joshi said neither he nor Tendulkar is satisfied with the recovery progress on the injury.

"The recovery has not been adequate," Dr Joshi told rediff.com

"The process has definitely taken longer than we expected," he said. "But these kind of injuries take long to heal."

Tendulkar suffered an injury that was diagnosed as tennis elbow during the Videocon [Get Quote] Cup tri-series in Amsterdam in August last year and made a comeback in the third Test against Australia in Nagpur in October after physiotherapy. Due to persistence of the injury he underwent surgery in London [Images] in May.

"Recovering from surgery takes almost double the time than regular treatment. That is because the muscle goes into a condition that's called 'disused atrophy'. Since the muscles are immobile it prolongs the recovery process," Dr Joshi said.

Strength loss is supposed to be the most evident response to atrophy.

"We need to do a lot of strengthening exercises. His forearm needs to get the strength back, because that is most important while batting. We are working on it," Dr Joshi added.

Adding that the injury itself has healed, Dr Joshi -- who is head of the Board of Control for Cricket in India's medical panel -- felt it would take time before Tendulkar returns to prime physical condition.

"It would be difficult to pinpoint when he can make a comeback," said Dr Joshi, who examined Tendulkar on Tuesday. "We will re-assess his progress in 10, 15 days."

Indian physiotherapist John Gloster, in a report to the BCCI, said Tendulkar is not confident or strong enough for the rigours of Test cricket.

'Tendulkar has returned to light net sessions, but he doesn't feel confident and strong enough yet to return to the rigours of Test cricket batting,' Gloster said in his report.