The midfielder was sent off for a crazy tackle on Adam Chicksen in the Black Cats' 2-0 Capital One Cup third round win at MK Dons and Gardner feels it is vital that the team sticks together and supports their mate.
"I feel sorry for Catts because he's been brilliant all season. His attitude in training and on the pitch is spot on. He's a true leader and I just feel sorry for him," Gardner told the Sunderland Echo.
"He's the last person in the world who wants to get sent off. He was rock-bottom in the dressing room afterwards and everyone was trying to pick him up.
"Hopefully we will get him back in the team. From where I was standing at right-back, it didn't look too bad. But I could be wrong. He was the other side of the pitch. "We have got to get behind him and lift him up."