Tim Henman believes Andy Murray's "hunger and desire" to return to the top have fuelled his comeback, but admits it is impossible to know if he will be able to get back to his best.
Murray claimed his first ATP Tour victory since January 1 on Tuesday, beating Tennys Sandgren at the Zhuhai Championships. He will play Australian Alex De Minaur in the round of 16 on Thursday.
The 32-year-old, who underwent a potentially career-ending hip resurfacing operation at the end of January, had previously faced Sandgren in the second singles match of his comeback in August, losing in two close sets. His latest victory then was a demonstration of the progress he has made.
Henman, though, says Murray needs plenty more matches before it might become clear how far that progress will go.
He told the PA news agency: "No one knows. He doesn't know, his surgeons don't know, his doctor doesn't know, but he's the one that's going to try.
"Certainly, knowing him as I do with his hunger and desire and motivation, if anyone can get back there I think it will be him, but it's going to be a challenge.
"No one has done this type of thing with the operations that he's had and I think he needs probably another six to eight weeks of tournaments just to build up not only the strength but the confidence in his body.
"January next year we'll probably get a clearer indication of where he's at."
As part of his recovery, the former British number one stepped down to the Challenger Tour, playing his first tournament at the second-tier level for 14 years in Majorca during the US Open.
Speaking as part of Jaguar's official vehicle partnership with Wimbledon, which saw the Jaguar ambassadors lead a tennis masterclass for a group of Ace Pace competition winners, Henman added: "I hit with him in May and he was only doing static stuff, he was standing in one corner hitting shots.
"But it's the movement that's the challenge and you see how much improvement there's been on the doubles court at Queen's and then playing doubles at Wimbledon and the challenger in Spain, he's moving in the right direction.
"It's just how much more improvement is there going to be really? We don't know.
"There are lots of people that have had new hips, but not at the age of 32 and who are then trying to play professional tennis, so we've just got to wait and see a little bit."