Manager Aidy Boothroyd admitted that he didn't see the offence properly and will look at video evidence before deciding whether or not to appeal the decision.
"I haven't seen the red card yet but I was as surprised as everyone else when he was sent off," Boothroyd said after the goalless draw at Vicarage Road.
"I'm going to have a good look at it before I decide whether to appeal or not.
Should Watford not appeal, or fail at appeal, then Eustace will have to serve an automatic three game suspension.