Andy Murray’s competitive return has been delayed, raising fresh doubts about his participation at Wimbledon.

The former world number one has not played since he was knocked out of the Wimbledon quarter-finals last July due to a hip injury.

Murray insists he remains hopeful of returning at this year’s tournament, but the Scot has now pulled out of his planned comeback event in Hertogenbosch, Holland, which starts on Monday.

Having only returned to the practice court over the last couple of days, Murray faces a race against time to be fit for Wimbledon on July 2.

“It is with regret that I won’t be ready to play in Hertogenbosch,” he said.

“I was excited to play there for the first time, but I am not quite ready to return. I am still aiming to play in the coming weeks, but I want to be 100 per cent when I do return.”

Murray underwent hip surgery in Australia in January after pulling out of the Australian Open.

The 31-year-old will make a decision on whether he will enter the Fever-Tree Championships at Queen’s Club, which begins on June 18, next week.

Earlier, in a promotional video for Jaguar, Murray spoke about the lengthy absence which has seen him lose his position as British number one to Kyle Edmund and drop to 47 in the world.

“It’s been very slow, I’ve been out getting close to a year now which is a lot longer than I expected at the beginning,” he said.

“I’m getting closer to playing again, I’ve started training a few days ago, hoping to make my comeback during the grass court season.”

Despite Murray's determination to play again, especially at his home Grand Slam, tennis legend John McEnroe has a serious word of warning for him.

“I carried on for about seven years - that’s a long time,” said the three-time Wimbledon, now 59.

“You keep giving yourself reasons as to why it’s worth it, the upside. You know: ‘It’s worth taking semi-humiliation’. You are still out there doing something you love in a way. You’re not as good as you were.

“I’m not even saying he won’t be. I don’t know what will happen, but it will be pretty tough to come back and be better than he was, unless I’m missing something when you have hip surgery.

“It’s worse, for me personally, to not even be able to play and not participate than, say, lose and you drop to 10 in the world. Even the last Wimbledon I played [in 1992 when he reached the semi-finals], I still had myself thinking ‘I could do this’.

It’s just a different animal. He’s going to play because he loves to play, but I’m sure he would be realistic about what he could do if he did play.

“It would be tough to go a long way if he hasn’t played. When you have a hip problem you have a tendency to be more cautious. I had some hip issues, I felt like I lost some speed. It’s not a good feeling particularly when guys are hitting it harder than ever even when I was playing.

“And Andy, it just seems like every time they can harry, they are just going for it. If you are not feeling quite right it can be tough, it’s too bad.

“How can he know he is 100 per cent? You got me, there is no way to know. You play practice and we all know how different practice is to a match where you step on the centre court at Wimbledon.”