The Ghanaian was replaced by David Brooks after 76 minutes having had a good performance to that point.
Semenyo struck the post in an early chance for the Cherries, after he headed on a long ball from Kepa to Evanilson, who flicked it onwards to Justin Kluivert.
The Dutchman then headed through for Semenyo, who shot first time, but saw his shot go agonisingly wide, striking the post and going behind for a goal kick.
Asked if Semenyo had picked up an injury and needed to be replaced, Iraola said: “No, he felt some tightness.
(Image: Richard Crease) “Straight away I asked him, he felt I can continue, but I feel some tightness. Obviously I decided to take him off straight away, not to risk him.”
The Basque boss said he was hopeful that his side hadn’t lost anyone to injury against the Hammers, after a first half scare as Evanilson went down after landing awkwardly jumping for a long ball.
Iraola said he was afraid that the Brazilian had injured himself, but he said: “He recovered well, he played very well.
“So I hope, because we are now in a difficult moment with the injuries, that hasn't cost us any other injury today.”
Bournemouth are without first team players Alex Scott, Luis Sinisterra, Julian Araujo, Marcus Tavernier and Marcos Senesi.
The latter two were recently ruled out for a spell, the Argentine undergoing surgery on his quadricep.
Last week, Iraola confirmed that Sinisterra will be the next back involved, but that the Colombian’s recovery hadn’t gone as quickly as the club would have liked.
Scott and Araujo both had surgeries earlier in the season, and will not be back before 2025.