West Brom coach Keen: No derby doubts over Popov
Keen says the 28-year-old has impressed his new coaches and team-mates.
"We had no doubts about him, even with it being a derby," said Keen.
"He has played Champions League football and you can see in his demeanour and the way he handles himself around the place, this is not a chap who is going to be fazed by anything.
"So we had no doubts on that front and the way he performed on Sunday shows he is going to be a great addition to the squad and he will certainly put some of our defenders under pressure for keeping their places, which is great."