Stan Wawrinka is struggling to return to fitness in time to defend his US Open title later on this month.

The world No 4 has not appeared on court since he lost in the first round of Wimbledon in early July when he was defeated by Daniil Medvedev.

Wawrinka has been suffering from a knee injury in recent months and it has led to him withdrawing from the hard court tournaments in Montreal and Cincinnati ahead of the Open at Flushing Meadows.

Earlier this week he posted on Facebook saying, “After much backwards and forwards and consultations with my doctors and my team, unfortunately I have decided to skip Canada and Cincinnati to be on the safe side even though I’ve been battling hard to make these events.”

He said that it was a “hugely disappointing” decision to make, for him and his fans. But that he wants to be absolutely fit before he resumes competition and make sure that the injury has completely healed. He said that his team is doing everything possible to make the recovery time as short as possible.

The US Open, the final Grand Slam event of the season, will be starting in New York on August 28 so he still has a few weeks.

He isn’t the only high profile player suffering from injury. Novak Djokovic has already called time on the remainder of his season because of an elbow injury so won’t be participating and earlier this week Maria Sharapova was forced to withdraw from her second-round match at the Bank of the West Classic in California. She pulled out of the encounter after taking medical advice following some pain in her arm. This comes soon after a hip injury and she will be focusing her energy on making sure she is fit by the end of the month.