Hull KR will be without back-row forwards Kevin Larroyer and Jordan Cox for around six weeks after they both suffered fractured ankles in Sunday's 54-12 defeat at Castleford Tigers.
France international Larroyer has started all 16 matches since joining the Robins on a season-long loan from Catalan Dragons while Cox has missed only four games so far this year.
Coach Craig Sandercock said: "It's very disappointing to lose both Kevin and Jordan for that amount of time.
"Kevin has been one of our best players this season and Jordan had just come back into the team, so for them both to suffer the same injury within a few minutes of each other is a blow for us.
"They are both important members of our pack but they will be in very safe hands with our medical team and hopefully we'll get them back on the field as soon as possible."