Roberts had only been on the pitch for 10 minutes when he received a red card for an alleged off the ball incident with Jonas Olsson.
Roberts and Allardyce were both bemused by the sending off which means that Roberts will miss the first three games of next season although the club will appeal.
Allardyce said: "The referee said Jason had been sent off for punching Olsson.
"It is not a punch. It is not even an elbow in the face. He has swung around to get his arm away from Olsson, who is having a tug at him.
"I have had a look at it on the laptop and I cannot see how it is a straight red card.
"Jason is looking at missing three games unless common sense prevails and the appeals committee agree with my view on it."