Sources close to the striker - the subject of a failed Chelsea bid earlier this summer - this month revealed he had been left "angry and confused" by United's treatment of him since the end of last season.
United are adamant Rooney will bot be sold, but Moyes spoke this month of how Rooney would be needed this "if for any reason we had an injury to Robin van Persie."
And Souness, a panellist on the Sky Sports Football Season Preview show, said he can understand why Rooney was left angered by his manager's comments.
He said: "Whether it was intentional or unwise words by David Moyes, if I'm Wayne Rooney I'm thinking 'hang on, I'm the star of the show'.
"He sees himself as now second fiddle to van Persie. He will be a very unhappy young man at that - his ego's been dented.
"Manchester United have put themselves in very difficult situation, but I don't think they can sell him to an English team."
Rooney, who has been undergoing treatment for a hamstring injury, is expected to return for the August 6 friendly against AIK in Sweden.