"It's a shame but I can't grumble because I've played a lot of games and not had many injuries - I've been lucky," he told BBC Radio Lancashire.
"It's disappointing, but sometimes you've got to listen to your body."
Mullin scored in his final game for the Shrimps in
February's 3-3 draw at Northampton.
He said: "It would have been nice to go out with a fanfare rather than a whimper but what else can you do?" he added.
"It's been great here, there's a good team spirit which reminds me of Accrington and I look back at my time with a lot of satisfaction."
The former mortgage advisor
joined Morecambe in 2009
on a free transfer from Accrington,
where he played 453 games in two separate spells
either side of a non-league career with North West clubs Darwen, Trafford, Clitheroe and Radcliffe Borough.
Shrimps manager Sammy McIlroy said: "He's been absolutely fantastic for me - a credit to the game, he's done us a great job for us and I think the big man will be taking stock in the summer and look at his fitness.
"I can see him going part-time and whoever gets him or takes him, will have a diamond on their hands."
Mullin's retirement comes five years to the day since he scored the goal that won
Stanley promotion to the Football League
at Woking in April 2006. He also
made six appearances for Bradford
during a brief loan spell in 2009.
"I'm seeing the specialist again on Monday so it's wait and see but I'm probably going to go back to my financial advising career," he said.
"I've a few things in the offing but if I can carry on playing in come capacity I'd like to because other than my back my body feels OK."
Source: BBC Sport
Source: BBC Sport