The flashpoint during United’s 2-1 win over the Hammers left the debutant full-back with a black left eye evident as he left the ground. Shaw refused to comment on the allegations but sources close to the incident claim it was the result of a head-butt from the Senegal forward.
It is believed Shaw reported the incident to an assistant referee but he, and referee Lee Mason, took no action. But video footage of the incident could yet see the FA take retrospective action for an alleged foul that would have brought an automatic red card for violent conduct if it had been seen.
Sakho scored the West Ham goal and was also booked, for a bad, late challenge on Rafael.
United skipper Wayne Rooney was not so fortunate and himself saw red for a late professional foul on Stewart Downing.