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.
Giggs gave an emotional speech to the Old Trafford crowd after the game.
But the Welshman is yet to decide whether he will stay at the club next year, when Louis van Gaal is expected to be in charge.
"Nothing has changed," Giggs said.
"I've not decided about my future.
"I'll wait until the end of the season."
When asked whether United were any closer to appointing their new manager, Giggs said: "I have not spoken to (executive vice-chairman) Ed (Woodward) for the last couple of days so nothing has changed since Saturday.
"It could be the next few days, it could be the next couple of weeks."
Wilson, 18, stole the limelight from Giggs by volleying home Marouane Fellaini's knock-down before adding a second after the break.
Wilson is highly regarded at United. The striker, scouted by the club when he was just seven, has impressed with the Under-21s this year and he scored on his Under-18 debut while still only 15.
"He is a natural goalscorer," said Giggs, who has played with his fair share of top strikers at United.
"But he has got more to his game than that. He can run at people, he has got pace and he is a clever player so I am delighted for him to score the two goals.
"He was fantastic."
Giggs also handed a debut to 20-year-old forward Tom Lawrence, who performed well.
Bruce, a former United captain, was impressed by the young players on show.
"They have got some good young players," the Hull boss said.
"Januzaj is 18 and if he keeps his feet on the ground, which I am sure he will do, he is going to be a superstar.
"Whoever gets the (manager's) job, I wish them the best of luck."
Other than a 25-yard strike from Matty Fryatt, Bruce's team had a night to forget.
Although United were not at their best for most of the match, the Tigers failed to test David De Gea often and their defence always looked vulnerable to the pace of Januzaj.
Bruce's team have conceded 14 goals in their last five matches and the former Birmingham boss wishes his team were in better form ahead of the cup final.
"It is a concern," Bruce said when asked about his leaky defence.
"Since we got through from the semi-final, that has been my hardest problem - to keep everyone focused on what's ahead. We need the cup final to come along quick but we will be ready for that."