Chelsea are investigating suggestions that a steward was hit by an object hurled by a fan in the Matthew Harding Stand following Manchester United's controversial third and winning goal.
After Javier Hernandez had poached the winner 15 minutes from time, a steward appeared to collapse.
He was surrounded by what appeared to be paramedics and taken away to hospital.
During Chelsea boss Roberto Di Matteo's post-match press conference a Chelsea spokesman said of the incident, that they believed that a steward had slipped and fell and hurt his knee.
Internet comments from fans at the game suggested that a chair had being hurled onto the pitch and that the steward was struck.
In a further update Chelsea added: "We are investigating all the incidents around the game and are looking at reports of objects being thrown.
"The steward was taken to hospital with a knee injury."