Hull FC scrum-half Sean Long has been ruled out until June after undergoing surgery on a broken thumb.
X-rays revealed that he sustained a fracture during the 36-18 home victory against rivals Hull KR on Good Friday.
Hull coach Richard Agar said: "It's a blow for Sean and for the team, as the derby game showed what a quality player he is and how vital he is to our team.
"But we have good cover in Sam Obst. He has delivered consistently well for us, both at hooker or in the halves."
Long initially believed he had suffered a dislocation and played on in the game at the KC Stadium.
But Agar confirmed: "He has a Bennett's fracture in his thumb and had an operation so we are looking at about six weeks and we'll see how he goes."
Earlier this month, Long was banned for two games and fined £300 after being found guilty of striking with his elbow against Castleford.