The Japan winger, who has lit up the Amex Stadium for much of the last two campaigns, has suffered a back injury which could leave him on the sidelines for three months.
He has already missed a chunk of the season due to an ankle injury and his participation in the Asia Cup.
Mitoma’s prolonged absence will be a big blow in the Seagulls’ quest for a top-six finish in the Premier League, their Europa League campaign – where they play Roma in the last 16 – and their FA Cup challenge, which continues at Wolves on Wednesday.
Boss Roberto De Zerbi said at a press conference to preview the trip to Molineux: “It’s a bad, bad situation.”

9. Billy Gilmour - suspended
The Albion midfielder received a harsh red against Everton and is suspended for Wolves, Fulham and Nottingham Forest. Photo: Warren Little