Tunnicliffe is a loan target for Ferguson.
"I have seen Ryan in action and he is a very good player," the Posh boss told The Peterborough Evening Telegraph.
"But I don't even know if United are going to loan him out anywhere. Ryan has not been sent out anywhere in his career, but he is already a very, very good player. He is one of numerous players I have shown an interest in, but that's as far as it's gone so far."