The Anfield based club are going through a period of transition with Roy Hodgson replacing Rafael Benitez after they could only manage a seventh place finish last term.
However Hodgson has already persuaded England midfielder Joe Cole to sign up after his contract ended at Chelsea and Giggs believes their rivals deserve respect.
"Liverpool have a new manager and difficult to say what they are going to do, " said the Welshman.
"Two years ago they were close to winning the Premiership and you can never write them off. It just depends on how it goes.
"It is dangerous to write off a team with Liverpool's history. They have won the same amount of leagues as us. You cannot just dismiss that. They are a huge club and a massive team."