Liverpool last won a league title, 21 years ago.
“Liverpool went off the radar for a bit. They are now back on it,” he said.
“Long term you know they are going to there.”
Ferguson admits Arsenal, Chelsea, Manchester City and Liverpool are all rivals.
“Let’s be honest, you hate losing to any of them,” he said.
“One of those four will always be a thorn in our flesh. They are our immediate challengers. History doesn’t change.
“No matter where it comes from, somewhere along the line we are going to be faced with a big challenge from one of those four great clubs.”
