"The problem is that there will always be speculation and I don't think it's right to talk out of school when it's about somebody else's player."
Blackwell has been trying to sign Latics winger Cotterill, who spent three months on loan with the Blades last season.
However, Blackwell is weighing up alternatives to the Wales international after being unable to conclude a move for the youngster.
"We're struggling to get something done there," he added.
"But there are about 25 right-sided players where enquiries are ongoing and we will pick one up if we think it's right."