Popov was sent off during Albion's home clash with Tottenham on Sunday after spitting in the direction of Spurs defender Kyle Walker.
The Macedonian international now faces a three-match ban and Baggies head coach Steve Clarke confirmed the player will face disciplinary action.
But Johnson is calling for a longer ban to apply to any player who acts in such a manner, and said: "I personally think it should be more. You see some people receiving a red card for trying to make a genuine tackle. You do something like that which is disgusting. No man should be faced with that. Personally I think the ban should be more."
Clarke condemned the behaviour of the on-loan Dynamo Kiev player in the aftermath of Albion's fifth defeat in six matches.