City beat Peterborough 2-1 despite former Brighton defender El-Abd dismissal after an off-the-ball clash with Posh forward Britt Assombalonga after just 20 minutes.
Fortunately City were already 2-0 up by then thanks to Sam Baldock's brace, and despite playing against 10 men for 70 minutes Posh could only pull one back through Michael Bostwick.
And Cotterill said: "If we had kept 11 men on the pitch we could be talking about a bigger victory.
"We started the game very brightly, as we knew we had to do, but I'm disappointed we picked up a red card.
"I need to have a look at the incident again to decided whether or not we will appeal.
"If the assistant referee who spotted it is proved correct, fair play to him.
"It turned into a long 90 minutes for us and those great late saves from Frank won us the game.
"I'm delighted for him because he is an absolute diamond.
"The table is starting to look a lot better and we can hopefully enjoy the rest of the season."