Australian utility-back Jake Mamo has retired from professional rugby league because of a back injury, Castleford interim boss Andy Last has confirmed.
Mamo's last appearance for the Tigers came in round two against St Helens when he was replaced mid-game.
The 28-year-old scored 69 tries in 133 games in the National Rugby League and Super League for Newcastle, Huddersfield, Warrington and Cas.
"Jake has been suffering a little bit," Last told BBC Radio Leeds.
"Because of medical reasons and how he's feeling with his body, he's made a decision that he's going to retire from top level rugby league which came as a bit of a shock."
Gosford-born Mamo was a youth player of some promise at Newcastle Knights and played for the Junior Kangaroos before making his NRL first-grade bow.
He operated at full-back, winger and centre during his career in the northern hemisphere, winning the Challenge Cup with Warrington against St Helens in 2019.
However, a series of knocks over the past few seasons have resulted in an early termination of his playing career.
"He had a few concussions over the past couple of years, and he's not been able to shake off the back injury," added Last.
"He didn't show any signs he was going to come to this decision, he got through pre-season ok.
"He's got some scarring from a mental point of view in terms of injuries he's picked up earlier in his career and those have impacted him moving forward."
Mamo told the Castleford club website that he "couldn't move for three days" after his injury against Saints.
"Rugby league has given me a lot and also given me the chance to move over here to the UK," he said.
"I've had good relationships with fans at all the clubs I have been at and that is going to be the thing I miss the most.
"I look back on my time at Cas fondly and I have enjoyed my couple of years at the club but felt this was the right decision for me moving forward."