Brighton forward Jamie Murphy will be banned for three games after the Football Association rejected Albion's appeal.
The 26-year-old was sent off for a challenge on Neil Danns in the 2-2 draw with Bolton Wanderers last Saturday.
Murphy will now miss matches against Cardiff, Leeds and Bristol City.
"I find it hard to understand. He slipped, there was no obvious intent and no strong contact," Seagulls boss Chris Hughton told BBC Sussex.
"I was confident we would get the decision we felt would be the right one.
"It seems incredibly harsh for a lad who has never been sent off before. There was nothing malicious."
Murphy was shown a straight red card by referee Mark Haywood and Hughton said after the match he felt the official was influenced by Danns's reaction to the tackle.
"It was deemed as dangerous play," the 56-year-old added.
"I understand there can be an element of the referee seeing the incident at full speed, and that he might make a certain decision.
"There is a difference between a player slipping and dangerous or malicious play.
"We are going to be missing a player for three games who has been very good for us. We feel for him."