Welham, Rovers' newly-appointed vice-captain who only recently returned from seven months out with a broken ankle, will miss the Super League opener against Catalan Dragons on Sunday week.
"It's obviously very disappointing for the team and for Kris, especially as he'd worked so hard during the off-season to get himself back to full fitness," said coach Craig Sandercock.
"Any time that you lose a player of Kris' quality it's going to hurt you but I'm confident that somebody else will step into that role and get the job done.
"It's hard to pinpoint exactly how long Kris will be out for but our medical staff, as they do with every injury, will be working overtime to get him fit and well again as soon as possible."
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