Margetson started the first three games of the season in goal but was then dropped in favour of Tony Warner. City lost 4 of the next 5 games and Margetson was inline for a recall but he pulled up in traing before the Derby County game at Ninian Park and he's been out ever since.
"When I went to strike the ball, a tendon pulled away from my kneecap," he told the Western Mail.
"It was traced to two discs in my back which had prolapsed and were hitting the sciatic nerve, causing this pain to go down my legs.
"Yes, the timing was cruel because I was back in for the Derby game. That did make it difficult for me to handle. Having said that, I've been very lucky with injuries during my career. It was the first major injury I've had and I'm in my 17th year as a goalkeeper.
"This is the first time I've had to deal with being out injured for a long time whereas other players have been very unlucky with injury."
Now Martyn, 34, has the gloves back on and is looking to fight for his place back.
It's the second goalkeeping story this week. The first came on Saturday when for the first time in over a year Neil Alexander made a league start. The young Scot had been told his future was maybe away from Ninian Park but with Margetson's injury Alexander found himself on the bench every game covering for Tony Warner. A gaff by Warner at Blackburn was enough to force Lennie into recalling the only keeper to keep three clean sheets through a play off campaign when he kept out Bristol City twice and QPR in the final.
Alexander returned to keep a clean sheet in the 2 - 0 win over Burnley.
"The gaffer told me during training on Friday morning that I was playing. I was absolutely delighted," said Alexander.
"I wasn't expecting it. I've learned not to expect anything from this game because there have been times when I thought I would get my chance again but it never happened.
"After being out for a year, I was nervous before the game. The conditions, which were appalling, only added to my nerves. It was wet which made the ball slippery so I had to really concentrate. It was so nerve-wracking, I felt like I was making my league debut all over again."
"It was a big game for us and I needed to do well, but the boys in front of me did a fantastic job and that made it a comfortable game for me.
"When the final whistle went, I was both relieved and delighted."