Just a week after learning that Gareth Williams had suffered an anterior cruciate ligament injury, Francis has sustained the same injury.
"It's a big blow, because I've been really pleased with him and I thought he was really starting to come into form," manager Aidy Boothroyd told the club's official website.
"Such is the game, this year we did really well with injuries and now all of a sudden we've had a few. That's life.
"It was an innocuous little stretch, he hyper-extended his right knee and felt it go a little bit. It's the same injury as Williams."