Wayne Rooney and Paul Scholes were sent off during Manchester United's 3-1 friendly win over FC Porto on Friday.
Rooney was sent off for the fourth time in his career
Both had scored before Rooney was shown a red card in the 42nd minute for allegedly elbowing Pepe.
Scholes was dismissed for a second booking on 68 minutes but United added a third through Ole Gunnar Solksjaer before Porto scored a late consolation.
If referee Ruud Bossen reports the incidents, the pair could be banned for the start of the Premiership season.
United boss Sir Alex Ferguson felt Rooney did not deserve to be sent off for his challenge, which came as he jumped for a header.
Wayne was surprised - it was unfair because their player made a meal of the situation
"There is an element of Wayne's reputation going before him," Ferguson said.
"I do not know what the referee was thinking because only a minute before that Ole Gunnar Solskjaer was elbowed and he didn't even warn the player.
"I do not see the difference between what the Porto player did and what Wayne did apart from one of the players is called Wayne Rooney.
"Wayne was surprised. It was unfair because their player made a meal of the situation but unfortunately that sort of thing is endemic in our game now."
But Ferguson did not defend Scholes, adding: "There is no excuse for Paul. It was a tackle from behind."
Ferguson now faces an anxious wait to see whether Rooney and Scholes will be banned for his side's first Premiership game of the season against Fulham on 20 August.
If Dutch referee Bossen notes the incidents in his report to the Dutch FA, and they pass it on to their English counterparts, the pair will almost certainly be suspended - with Rooney facing a three-game ban.
Rooney was also sent off in his last competitive match, for England in their World Cup quarter-final defeat by Portugal on 1 July.
He was being watched against Porto by new England coach Steve McClaren who is preparing to announce his squad for his first game in charge, against Greece on 16 August.
Rio Ferdinand was on the United team sheet but landed heavily on his right ankle during the warm-up and was left out as a precaution by Ferguson.
The incidents completely overshadowed new signing Michael Carrick's first game for United but he made an impressive debut.
Carrick's corner was rifled home by Scholes on the edge of the area for United's first goal before Rooney's audacious chip made it 2-0.
Solskjaer slammed home a third when United were down to nine men before Pepe's late reply for Porto.
The game was United's first in a four-team tournament that also features Ajax and Inter Milan.