Morgan, 34 made 281 appearances for the Blades in all competitions after signing on a free transfer from his hometown club Barnsley in July 2003.
He told BBC Radio Sheffield: "There comes a time where you have to be honest with yourself. I've decided that enough is enough and I think I've made the right decision."
He added: "Right from the word go we never got on top of the injury. No matter what we tried it just didn't seem to work and the surgeon agreed this is the right time. I don't want to get to 60 and not be able to walk."
The former defender spent last season as Reserve Team Manager and was highly successful; winning the league and is expected to carry on his coaching role this term.
Source: FOOTYMAD
