The Baggies defender was shown a red card early in the second half for spitting at Spurs right-back Kyle Walker as the pair exchanged heated words and now faces a three-match ban.
Popov, the Macedonian international, will also face disciplinary action from his club as confirmed by Clarke following the match.
"The game changed with the sending-off. I'm absolutely disgusted with Goran's behaviour," said Clarke, whose Albion side lost to a brilliant Gareth Bale strike in the 67th minute.
"One of the group has let the players down. It changed the whole complexion of the game.
"It's difficult enough in the Premier League playing against 11 players, especially when you're playing against Tottenham.
"There's no excuse for that. There's no place for it in life, never mind on a football pitch.
"I would like to think that at some stage he will apologise. As always there will be disciplinary procedures taken against the player but they'll remain in-house."