The Daily Mail says Sheffield United want to sign the 24-year-old immediately and have seen an offer in the region of £100,000 rejected by the Tannadice club.
It's thought United would want more than double that amount before being persuaded to part with him during the current transfer window.
Meanwhile, Celtic No2 John Collins said: "He's a good football player. He's got pace, he's skilful, but he's a Dundee United player. We're looking for speed in the wider areas and at the top of the pitch. It's very important and if we can find that it would obviously be very good for us."