The Belgium international received a second yellow card after referee Michael Oliver deemed that he had intentionally delayed the game at the Etihad Stadium.
Initially, the foul was awarded to the Citizens after Trossard barged into the back of Bernardo Silva, but he was shown red after kicking the ball away in the aftermath of the tackle.
The latter offence, which was an infraction for which Declan Rice was also sent off against Brighton & Hove Albion last month, left Mikel Arteta's side with 10 to defend a 2-1 lead.
Unfortunately for the Gunners, John Stones ultimately breached their resolute defence with a strike in the 97th minute, bringing the intense match to a close with a 2-2 scoreline.
Trossard insists he had not seen referee's signal
Following his sending off, Trossard insisted to his teammates in the locker room that he had tried to make a pass and had not seen the referee's signal, as reported by The Mirror.
The report adds that the 29-year-old attacker even attempted to explain to the match official that he had not heard the whistle before receiving his marching orders.
Referee Oliver faced a similar situation and did not issue a yellow card to Liverpool's Dominik Szoboszlai for kicking the ball away during the Reds' home loss to Nottingham Forest, leading to accusations of double standards.
Arteta was clearly infuriated by the decision to send off Trossard but directed his frustration toward the officials rather than his player, and both he and his coaching staff embraced the Belgian as he walked off the field.
The result saw Pep Guardiola's side move back to the top of the Premier League standings and maintain their unbeaten start to the 2024-25 season, while the Gunners were left in fourth place, trailing the league leaders by two points after five games.
Trossard sending off one of many questionable decisions
Trossard's sending-off was just one of several controversial incidents from the match, with Erling Haaland's antics, the amount of added time, and the use of time-wasting tactics also prominent topics in the post-game discussion.
Haaland was widely regarded as extremely fortunate not to be sent off himself after he was caught throwing the ball at Gabriel's head following City's late equaliser.
Meanwhile, Opta stats indicated that the ball was in play for 63 minutes and 29 seconds, making it the fifth longest of any Premier League game this season.
This has led to confusion regarding the significant amount of stoppage time played on Sunday, with eight minutes added at the end of the first half and nine at the end of the second 45.
Fourth official Andy Madley had initially signalled for six additional minutes, but two more were played, with City scoring their equaliser in the 97th minute.