The red card shown to Bruno Fernandes during the Europa League tie between Porto and Manchester United cannot be overturned for one specific reason.
Fernandes was sent off in the 81st minute of United's 3-3 draw with Porto in the Europa League after a high boot earned him his second yellow card of the match.
It is the second time that the United captain has seen red in past five days, with Fernandes shown a straight red card for a foul of James Maddison during the 3-0 loss to Tottenham Hotspur last Sunday.
And, while the red card against Tottenham was later rescinded, this will not be the case for Thursday night's card due to one little-known rule.
Unlike the red card against Tottenham, United will not be able to overturn the decision to send off Fernandes during the Porto match as it is not possible to appeal against two yellow cards.
This means that the Red Devils will be without the midfielder for their next Europa League match against Jose Mourinho's Fenerbache on October 24.
The Turkish club won their Europa League opener over Union Saint-Gilloise, before drawing 1-1 with FC Twente on Thursday night.
Meanwhile United are yet to win a match in Europe this season, having drawn against both Porto on Thursday and FC Twente last week.
In fact, under Erik ten Hag, United have won just one of their last ten games in European competitions, losing five matches, drawing four and earning their solitary win over Danish side Copenhagen in October last year.
"We will get there," Ten Hag told TNT Sports after Thursday's match.
"Don't judge us in this moment, judge us at the end of the season.
"We are in the process, we will improve. We have had two seasons where we have reached finals, we will continue and fight."
The result leaves United 21st in the 36-team Europe League table, two points adrift from the top eight clubs that are guaranteed a place in the next round.