United need one point from two games after beating Chelsea 2-1 on Sunday in the Premiership.
Guardiola said: “They played a Champions League semi-final [second leg against Schalke] with a team full of reserves and they won 4-1 – that says everything you need to know about the quality they have,” Guardiola told the post-match press conference. “They have a great squad with two great teams and extraordinary players.”
