Andy Murray may struggle to rediscover his best form due to troubles with his hip, says Andrew Castle.
The Briton played a charity event against Roger Federer in Glasgow on Tuesday, his first public match since exiting Wimbledon in July.
After the event, Murray said: “I felt pretty good – not perfect but I felt like I’m going in the right direction.”
But TV commentator Castle said: “From the evidence of my eyes, it doesn’t look like his hip is good at all.”
Castle, 53, is a former British number one, and had a hip replacement in December 2013.
“The way he’s moving, changing direction, he’s clearly uncomfortable,” he told BBC Scotland after watching Murray take on Roger Federer and play a doubles contest with brother Jamie.
“I was disheartened to see that he hadn’t made much progress in terms of the way he was walking between points – more than four months on.
“I’m not trying to be negative and I was delighted to see Andy back out on the court, he’s given us so much joy over the years.
“To be quite honest, I’m just not liking what I’m seeing.”
Murray, 30, is a three-time Grand Slam champion and double Olympic singles gold medallist.
The Scot finished last season by winning the ATP World Tour finals and taking over at the top of the rankings for the first time.
However, his enforced inactivity has led to him dropping to 16th in the end-of-season standings.
“I’ll come back when I’m ready and 100% fit,” said Murray, whose wife Kim gave birth to their second child in recent days. “I believe I will get back to that.”
Castle, a mixed doubles finalist at the 1987 Australian Open, added: “I know he’s training hard and doing all the physical work.
“The fluidity of movement is certainly not there at the moment. Perhaps it won’t keep him off the court for ever. I’m not a medical person.
“He’s always kind of loped around, then burst into life during points. The physical element of his game has been extraordinary.
“He’s 30, he’s a father of two. He’s done so much. None of this will lessen his desire to get back but I didn’t feel positive watching him last night.
“If you can’t sprint or change direction, then it’s going to be very difficult.
“If that hip issue wasn’t there, he’d have another five or six years because he is such a thorough professional.
“If we’ve seen the last of him at the top level, then that’s a real shame.”