The former TFC forward has scored in both of his first two games since joining Chicago.
The Wales international grabbed his first goal for the club in its 2-2 draw with Toronto last week, and continued his inspired start with an 83rd-minute winner against Dallas. But while Yallop is undoubtedly delighted with the 33-year-old's form, he insisted it didn't come as a surprise.
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"I think the big thing for me when we signed Robbie was that he's already been in the league," the former San Jose and Canada boss said after the game. "I always felt that bringing in someone who has already played in the league is really important. He gets the travel, he gets the game, he gets what's good. Impact-wise, he's obviously been very key to us the last few games, so we're hoping it continues.
"If you look at Robbie's goal-scoring record, it's very good. He knows how to score goals; give him a service, he'll put it in net. Not surprised, but very happy. I think that's the key for me: Anytime you sign anybody, you just really hope it works out.
"Very happy for him, he's a great kid, and he works hard, and he's clued into what we want to do, so very good."
Chicago is currently 5-6-14, four points out of the playoff spots with a game in hand over fifth-place Columbus.