Mark O'Brien has been forced to quit football at 27.
The Dubliner was Newport County's captain but has been told he needs heart surgery.
O'Brien had previously gone under the knife in 2009 to correct a heart valve problem.
The ex-Derby and Luton defender was a cult hero for Newport after scoring the winner against Notts County that saved the club from relegation from the League in 2017.
He had previously battled back from a cruciate injury and a knee injury before joining the Welsh outfit three years ago.
"The club will be doing everything it can to support Mark at this difficult time," read a Newport statement.
