Nicolas Pepe says he is "deeply sorry" after being shown a red card in Arsenal's 0-0 Premier League draw with Leeds United on Monday (AEDT).
The 25-year-old was shown a straight red after 51 minutes at Elland Road for headbutting Ezgjan Alioski.
Pepe and Alioski received abusive messages on social media following the off-the-ball incident, which were later condemned by both players' clubs.
Gunners boss Mikel Arteta described the winger's actions as "unacceptable" and the Ivory Coast international has now taken to social media to apologise for his conduct.
"Yesterday I let my team down at a crucial time of the game and there is no excuse for my behaviour," Pepe wrote on Instagram.
"I am deeply sorry and would like to apologise to the fans, my teammates, my coach and everyone else at the club."
Pepe has struggled this season, with the game against Leeds marking just his second start in the Premier League.
He has scored once and created just two chances for his teammates, although one of those did lead to a goal.