"But he's going to be fine. It's not life-threatening."
Gilks was replaced by Richard Kingson at Upton Park and the Ghana international is expected to continue in goal when Blackpool host Wolves on Saturday.
Fellow keeper Paul Rachubka is fit to play but is ineligible as he was not named in the 25-man squad at the start of the season as he was suffering from a knee injury that was expected to keep him out until January.
Mark Halstead, 20, will be used as cover after being recalled from a loan spell at Barrow which he began last week.
Holloway also admitted to a concern over Charlie Adam, who sustained medial knee ligament damage in his 55 minutes of action during Scotland's 3-0 win over the Faroe Islands on Tuesday.
The 25-year-old midfielder is a doubt to play Wolves, with Holloway admitting: "I don't think he is going to be available, he couldn't train [Thursday] morning.
"But we will leave it right until the last minute Saturday morning.
"It is not as serious as they thought it was in the Scotland set-up but it does feel a little sore."
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