Immanuel Feyi-Waboso was sent off as Steve Borthwick's England XV conceded two late tries in a disappointing 26-24 defeat by a France XV at Twickenham's Allianz Stadium.
Feyi-Waboso, who missed the Six Nations and a possible place in the British and Irish Lions squad after dislocating his shoulder in December, caught Antoine Hastoy on the head with a swinging right arm as he attempted a tackle in the 34th minute.
Referee Hollie Davidson showed the 22-year-old a yellow card and asked the television match official to check the degree of danger and whether there was any mitigation.
After a straightforward review, the card was upgraded to a 20-minute red, which allowed England to bring on a replacement when the time expired, but leaves Feyi-Waboso facing the prospect of a ban that could rule him out of England's tour of Argentina and the United States.
"This is a good guy who just tries his heart out and has left the field today and it didn't go the way he wanted it to, so he's gutted in the changing room," said head coach Borthwick.
"Everyone will get around him and we'll find out about what the situation is in the next 24 hours."
A try from Harlequins captain Alex Dombrandt shortly after France's Cameron Woki was sent off gave England a 24-12 lead heading into the final 10 minutes.
However, Paul Mallez's try set up a frantic final five minutes and Romain Taofifenua burrowed over to tie the scores with the clock in the red.
Hastoy fired over the conversion to snatch victory with the last kick of an entertaining uncapped match played in sweltering conditions and watched by a crowd of 34,129.
Borthwick, who was without 13 England players selected in the Lions squad - including captain Maro Itoje - names his squad on Monday.
"We want to win, our supporters want us to win, and it is frustrating not to have got that win having been in such a good position," he told BBC Sport.
"Argentina are a better side - they've just beaten the Lions - so we need to focus fully on ironing out the bits that weren't quite right."
Six Nations champions France, preparing for a three-Test home series against New Zealand, were also without several key players because of the ongoing play-offs in their domestic league.