It has been something of an inauspicious start to the midfielder’s career in the Chelsea first-team as the dismissal followed his role in a 3-0 defeat at Leeds last week.
“Proud of the team for digging deep today and winning with 10 men,” he wrote on Instagram after the game.
“Personally, I want to apologise to my teammates, staff and the fans. I take full responsibility for the rash decision leaving them with a huge challenge for the rest of the game. Thankfully, they came through.”
Chelsea secured a nervy 2-1 win over Leicester after Raheem Sterling’s brace followed Gallagher’s exit, although coach Thomas Tuchel was not impressed with the youngster’s two bookings when speaking at full time.
“You can't make the challenge if you have a yellow card after 20 or 25 minutes,” Tuchel told Match of the Day.
“The challenge was a clear yellow card and gave us a huge disadvantage. There was no reason [for Gallagher] to make this decision.”