Macedonia international Popov said: "Getting the red card was very disappointing. This was a bad moment for me but everyone makes mistakes.
"I am not trying to make an excuse but I can say that I was surprised to get a red card. I spat in front of me, not at the player. I am not this kind of person.
"If I was in another country, if I do this in Ukraine or Holland, it is not a red card, but in England this is the way it is treated.
"I understand this, which is why I apologised to everyone, but it is over now. You learn from mistakes and it will never happen to me again."
Albion have the option to make Popov's move permanent after he made it clear that he wanted to leave Kiev.
Popov said: "West Brom wanted me last summer and I told the president at Kiev that if I had to stay for my contract, it would be hard for me to give my best form to the team.
"That is why I am here now on a one year loan and, at the end of the season, we will see what happens."