Hull KR boss Justin Morgan has signed former Wales team-mate Mark Lennon until the end of the 2007 season.
Morgan took Hull KR into Super League this season
Lennon, 27, made 51 Super League appearances for Castleford and is set to make his debut in Sunday's home clash with bottom side Salford.
"Mark is a very versatile player," said Morgan. "He adds a new dimension to the backs and, more importantly, he is available to play this weekend."
Lennon joins fellow loan players Ian Hardman and Danny Hill at Craven Park.