Diafra Sakho may face a Football Association charge after Luke Shaw suffered a black eye from an alleged butt from the West Ham United forward during Manchester United’s 2-1 win on Saturday.

The incident is thought to have occurred in the second half at Old Trafford. While Shaw could be seen complaining to the assistant referee, Andrew Garrett, it was shrugged off, with the left-back displeased with the response.

This may suggest that if Sakho did strike Shaw, as is claimed, it was not seen by either Garrett, the match referee, Lee Mason, or any of the officials. If so, this is would allows the FA to investigate if they deem there is a case to answer. This would be done by examining television pictures to discover if there is any conclusive evidence.

English football’s governing body expect to have Mason’s report on the match by Monday morning, so will decide if any further action is required then, and Shaw refused to discuss the incident. However, a source close to him claimed that Sakho had headbutted the defender during the game and left him unhappy over the incident.

Shaw may have hinted at the episode when talking of Wayne Rooney’s 60th-minute red card for hacking at Stewart Downing. “We have actually had a lot of bad luck, especially with Wazza’s red card, as I would say there was a handball before that but the referee didn’t stop play,” he said. “Earlier in the game, Sakho did the same to me but I just focus on winning games and I’ll keep doing that.”

If Sakho, a 24-year-old Senegal striker who scored West Ham’s consolation goal at Old Trafford, was found guilty of the offence he would face a lengthy ban. Chelsea’s Ramires received a four-match suspension for an off-the-ball incident in which he elbowed Sunderland’s Sebastian Larsson towards the end of last season. West Ham had not responded at the time of going to press.

Shaw was finally making his debut for United after arriving in a £27m deal this summer from Southampton. The 19-year-old had been ruled out with a hamstring injury and he conceded: “It was a tough debut, I would say. Obviously, we went down to 10 men and it’s never easy but we all fought hard and showed how much we wanted these three points. It means a lot to us. I’m glad we got the three points in the end. Overall, I’m really pleased with how my debut went but the main thing, for me, was to get the win.”

Louis van Gaal criticised Shaw over his fitness during the club’s summer tour of the US but the left-back stated he has a strong relationship with the manager. “Of course, he was right to say that,” he said.

“We had a discussion in pre-season and the plan for me was to get my fitness up. It worked, I think, apart from the injury. It was a bit of a setback but I’ve worked hard in the last weeks and had some talks. He’s been a great inspiration to me and hopefully I can carry that on. For him to say I’m an example at a massive club like this is something to be really happy about.”