The midfielder's current contract expires at the end of this season, meaning Sunday's game against Leeds could be his final for the club.
"I don't think it could have gone any better," said Frank. "People ask me 'are you surprised by his level?' No.
"I think maybe when I watch more games with him, training sessions, and watch the games back. I have a feeling that he plays with an extra edge.
"Of course I ask him about it. It just feels like he plays with a combination of freedom, that little extra determination. He's enjoying it.
"He's a maestro on the pitch. He's the one that dictates the games. He's always been running and covering a lot of ground but his recovery runs, his willingness to come back into the box and clear balls, heading balls away, that you have to do when you play for Brentford, has been remarkable.
"I haven't seen that from him earlier in his career. It seems like he, I don't know, maybe cares a little bit more about everything."
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