Interim boss Ryan Giggs lashed out at Hull's David Meyler for an alleged stamp on Adnan Januzaj in Manchester United's 3-1 win at Old Trafford.
Teenage debutant James Wilson scored twice and Robin van Persie also got on the scoresheet in what may have been Giggs' final home appearance in a United shirt.
But the gloss was taken off an emotional night for second-half substitute Giggs, and the departing Nemanja Vidic by an incident involving Meyler and Januzaj in the dying minutes.
Meyler sank his studs into Januzaj's shin as he lay on the floor after the two players had clashed going for the ball.
Giggs was annoyed that Januzaj was stamped on for the second time this season - Sascha Riether did the same to the young Belgian in November - and called for greater protection for the midfielder, who was named man of the match.
"It's a joke," the United interim player-manager said.
"I didn't see the incident, but I have seen his leg.
"It is the second time it has happened to him this season and it's not great to see. It's terrible, his leg.
"He needs protecting, he is a brilliant player, he is exciting and the authorities need to stamp down on it, whether that can happen now but it was bad.
"I have not seen the stamp but I have seen his leg and it is bad. The cut goes from his knee to his ankle."
Referee Craig Pawson did not see the incident, so Meyler could be punished retrospectively by the Football Association (FA).
The FA did so with Riether, banning him for three matches. If it decided to hand down the same punishment to Meyler, the Republic of Ireland international would miss Hull's FA Cup final against Arsenal a week on Saturday.
Hull boss Steve Bruce said he did not see the alleged stamp.