"We've made an enquiry for Barry in the last seven days but we were told he's not for sale," Souness told the Evening Telegraph.
"He's someone I've been aware of for a few years, he's still only 25, and I think he's a very, very good player.
"But Rangers told us that he's not available and that's the end of it.
"I've got a good relationship with the chairman of that football club and I respect what he says."