Paul Parker admits there are questions over whether Gary Neville will play again for Manchester United.
Former United fullback Parker told the Manchester Evening News: "I know exactly what Gary is going through and I think for him to return as the player he was for United would now be a hell of a comeback.
"But I also know how strong a mentality you have to have to get over these things and the desire to make it and he has all those qualities. I was in my 30s when my injuries struck. When you are in your 20s you can battle back better from a length of time out.
"But in your 30s, in fact at any age at a club at United's level, you discover how quickly things move on. I had an ankle injury and eventually that repaired after surgery but you start getting compensation injuries, which is what Gary is finding.
"When you've concentrated on the part of your body that has been injured the rest naturally weakens. So as you return you become struck down by strains, pulls and tweaks.
"After my ankle surgery I suffered my first-ever calf strain. Because I had been compensating for my bad right ankle as it recovered I put stress on my left leg. I ended up with a cartilage problem and then a couple more knee injuries.
"It's frustrating and you want to get back quickly because you know at a club like United that things have to move on. They can't wait around for people.
"You might think you are doing OK but you have really been stagnating while you've been out, especially when you are Gary's age.
"While I was sidelined United were going from strength to strength and it is extremely difficult to catch up. Your team-mates are getting sharper and sharper so you are actually going backwards. When I came back into the team I felt like I was playing on planet Zog in comparison to my colleagues.
"Mentally for Gary it will be extremely tough now because he is United's captain and as you come to the end of the season and trophies are on offer he won't want to be stood there in his suit watching someone else lifting the silverware."