Midfielder Aaron Mooy sustained a knee injury in training and has been rated at less than 50-50 to play against Carlo Ancelotti's team.
It's a blow for Graham Potter as Mooy, who is on a season-long loan from Huddersfield, has been one of Albion's best performers this season, particularly over the hectic festive period.
The 29-year-old Australian international also scored the club's December goal of the month with an excellent strike during his man of the match display in the crucial 2-0 win over Bournemouth.
He was rested for last week's FA Cup loss against Sheffield Wednesday with a view to keeping him fresh for the Premier League clash at Everton.
Potter said, "He has had a knock in training and hasn't trained for the last couple of days. We have to see how he is for the weekend. I would say he is less than 50-50."
Dan Burn is also unavailable following a fractured shoulder after a heavy collision with Reece James in the 1-1 draw against Chelsea on New Year's Day. Burn is said to be making good progress following his operation and will hope to be back after the winter break in February.
Jose Izquierdo (knee) remains a long-term absentee and Potter was reluctant to put a time scale on his return. The head coach also said he can't guarantee he will be back this season.
On the plus side, Solly March has recovered from a groin operation and has trained well this week. He was close to making the team against Sheffield Wednesday but is now in contention for Everton.
Potter added, "He has trained well and there is a chance he will be involved in the squad. He (Solly) has had an okay season but there is more to come from him."