Rankin was sent off in the latter stages of the 0-0 draw at St Mirren Park for a two-footed challenge on John McGinn.
"When you look at it again, I don't think it's so bad," said Rankin. "There's no malice in the challenge whatsoever and hopefully we'll overcome the appeal later in the week.
"To be fair to the referee he's right up with play and on top of it," said Rankin.
"I've read it, but none of my two feet are off the ground. I've tried to keep both of them on the ground and my studs aren't showing.
"The referee is right on top of it and he's got to make a split decision, but I think he's a bit quick with the cards."