McGregor was linked with Newcastle United and Tottenham during the summer.
Weir said: "It's probably a good thing Allan is playing so well.
"He's been outstanding for a long time now and that gives us confidence. I'm sure he'll need to be on top form for this game.
"I'm sure people are already aware of him in England - I don't think he's any secret - but I'm sure it wouldn't do him any harm to play well.
"He's quite happy where he is, though, and hopefully he'll be with us for a good time longer."