Barnsley have confirmed that their bid, of £200,000 has been sent to the Millers in writing after they had verbal contact with Rotherham about the players availability.
Boss Alan Knill commented this evening: "Barnsley have put in a bid for Lee but I don't think we would be in a rush to let him go there but the decision lies with Lee.
"The good thing about Williamson is that when he puts a shirt on for Rotherham he plays for Rotherham and he has no other thoughts and hopefully that continues."