Mark McCall said Maguire had settled well into the Ulster squad

The New Zealand-born back joined Ulster at the beginning of July but scans have revealed the condition which he was totally unaware of.

An Ulster statement said continuing his career would have "led to serious arthritis problems in later life".

The economics graduate intends to stay in Belfast in the hope of finding work.

The Ulster branch statement said Maguire had "never experienced anything more than some stiffness in the joint post-match or training".

"However the Ulster medical staff flagged up the trouble-spot during his medical and subsequent scans have revealed that Maguire has a condition which, unbeknown to either the player or any of his previous clubs, he has had since birth."

Ulster coach Mark McCall said that he was "very disappointed to lose Mike from the squad".

"He's settled in and trained very well since the start of pre-season however, he must look to his long-term future and we fully support his decision to retire from rugby," said McCall.