The English Football Association (FA) has sought observations from Derby County manager Wayne Rooney after he said in a recent interview that as a player he wanted to injure an opponent during a game in 2006, British media have reported.
"I changed my studs before the game," Rooney said. "I put longer studs in because I wanted to hurt someone."
"The studs were legal," he added. "They were a legal size. But they were bigger than what I would normally wear."
Rooney and John Terry clashed during the game, with the Chelsea defender receiving treatment.
United lost the match 3-0, with Chelsea winning the league that season.