The 24-year-old was sent-off by referee Bruno Paixao for an 80th-minute lunge in a 3-1 victory over Sporting Lisbon in Albufeira, and manager Roy Keane's angry protests to fourth official Nuno Campes saw him similarly despatched.
Chopra faces an anxious wait to see if he will be banned when the new Premier League season kicks off against Liverpool on August 16.
His hopes rest on whether or not the Portuguese Football Association report the incident to their English counterparts, who would then have no choice but to impose a suspension.
Keane: "There were a few tackles going in on our lads.
"I think Michael Chopra was very unlucky to get sent off and hopefully, not too much will come of it.
"Anyone who knows Chops knows he can't tackle. I suppose it was a typical striker's tackle - slightly mistimed.
"I thought a booking would have been the worst possible scenario, but unfortunately, he got red. We will see how it goes. Hopefully that will be the end of it."