Keen believes Thomas will be on a mission to prove Albion wrong.
"He played well last Saturday," the Baggies assistant boss told the Birmingham Mail.
"He's a good player, a good dribbler, he can score goals, create goals.
"We will be very much aware of what he's bringing. He will want to show that he should have got a contract. I'm sure the crowd will give him a great reception because he did very well."
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