Manchester United manager Sir Alex Ferguson has confirmed his belief that deadly rivals Liverpool are now "back on the radar".[LNB] It is now 21 years since the Reds last won a league title.[LNB]As their enemy from down the East Lancs Road were clinching a record 19th crown, Liverpool were finishing in sixth, 22 points adrift with not even a Europa League place to cheer them.[LNB]However, under Kenny Dalglish, Ferguson can sense a giant awakening from its slumber. And the Manchester United manager is prepared to concede they are a club to be wary of again.[LNB]"Liverpool went off the radar for a bit. They are now back on it," he said.[LNB]"Long term you know they are going to there."[LNB]It is the same with Arsenal, Chelsea and Manchester City, a rival in name - Ferguson did previously claim Liverpool was the true derby for his team - now in performance too.[LNB]"Let's be honest, you hate losing to any of them," he said.[LNB]"One of those four will always be a thorn in our flesh. They are our immediate challengers. History doesn't change.[LNB]"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."[LNB]Recent history for United is not particularly comfortable.[LNB]A summer that could have been spent basking in the glory of Liverpool being knocked off their perch has instead involved reflection on the Champions League final, and a chastening experience at Barcelona's mesmeric feet.[LNB]So clinical was the Catalans' victory it has almost been forgotten United went into the game having secured four Premier League titles out of five and were featuring in their third European Cup final in four attempts.[LNB]It should be one of the club's most notable periods. Instead the Red Devils are being written off as inferior.[LNB]Not by Ferguson. Not by a man who is forever plotting and scheming to give his side the best possible advantage. Not for a man who simply refuses to abandon the fight.[LNB]"Barcelona are the team of the moment," reflected Ferguson.[LNB]"It is a cycle. It is the same players. They can dominate any game and could have probably done that to any other team.[LNB]"But it is not the kind of thing that makes you think 'let's not bother with European football any more, we are never going to beat Barcelona'.[LNB]"Manchester United are bigger than that. We have a better philosophy than that.[LNB]"The challenge will be can we improve enough to get to the final next season - and win."