Nottingham Forest striker Taiwo Awoniyi underwent surgery for an abdominal injury on Monday after he clattered into a post during their 2-2 Premier League draw with Leicester City a day earlier, the club said.
Substitute Awoniyi rejoined the game after receiving treatment but was limping around for the last 10 minutes.
"The club can confirm Taiwo Awoniyi has undergone urgent surgery following an abdominal injury sustained during Sunday's match against Leicester City," a statement said.
"Everyone at Nottingham Forest sends their best wishes to Taiwo.
"The club will provide further updates when appropriate."
Forest owner Evangelos Marinakis expressed frustration over Awoniyi not being substituted, with manager Nuno Espirito Santo saying the Nigeria international was left on due to a misunderstanding between the coaching and medical departments.
Forest, a point behind fifth-placed Chelsea, visit West Ham United on Sunday.