The 30-year-old was sent off in stoppage time by referee Graham Scott after a challenge on Iheanacho.
However, Success said that his countryman confirmed to him that there was 'no contact'.
“I spoke to Iheanacho and he said there was no contact by Capoue,” Success told club website.
“I feel sorry for him because he has been one of our best players. Let's see what the FA will do because it was never a red card.”
Prior to the incident, Capoue had scored two goals across all competitions this season and has been a consistent fixture for Watford featuring in all but one of their Premier League games.