Sid Domic has agreed a compensation deal with Hull FC after being removed from their overseas quota to make way for Australian half-back Matthew Head.
Domic made 37 appearances since joining Hull in 2005
Super League clubs are only allowed three overseas players in their squad.
The 31-year-old Domic was in his second season at the KC Stadium but had already announced his intentions to retire at the end of the season.
"This was one of the toughest decisions I have had to make," admitted Hull coach Peter Sharp.
"Unfortunately, in life you sometimes have to make a decision you'd rather not and this was one of those occasions."
Hull are taking St George-Illawarra's Head on loan until the end of the season.
Hooker Richard Swain - who will also retire at the end of the season - and winger Matt Sing are the other players on the quota.
Domic had been out of action with a hamstring injury, rendering him all the more vulnerable to be cut from the squad.
Sid can look back on his career with pride
"It is probably fair to say his hamstring injury came at the wrong time, especially as he is expected to be out for several more weeks," added Sharp.
"The disappointing thing is Sid is not finishing the way anyone would want him to end but sometimes that's not possible.
"The one things Sid can do is look back over his career here in England and at home in Australia with pride.
"Sid doesn't owe anybody, or himself, anything because he has been a tremendous professional, a dedicated one, totally committed and someone who you could always rely on to give 100%."
Domic's contract expired at the end of the season, and the club said it had agreed a settlement package which "fully compensated" him for his removal from the squad.
Hull chief executive James Rule said: "It was an extremely difficult decision but we felt it necessary in the light of the need for a leader and direction on the field.
"Before we made this decision we explored every domestic option before carrying out our search overseas and now we are confident Mathew Head will provide the leadership and direction we have been looking for."
Domic, who has also had spells with Super League sides Warrington and Wakefield, scored Hull's only try in the 2006 Grand Final.