PSV remain the favourites to qualify for the Champions League group stage after playing out a 2-2 draw at Ibrox in the first leg of their playoff tie.
Rangers are the underdogs going into the second leg at the Phillips Stadion on Wednesday night, but Gullit stressed that it would be a mistake to take the Glasgow giants lightly.
He insisted that PSV were not great in the first leg and created very little despite dominating the ball at Ibrox.
He pointed out that the onus is on PSV to take the game to Rangers as the away side can afford to wait for the Dutch giants to make mistakes and take advantage of them.
Gullit said on Dutch broadcaster Ziggo Sport: “I think you are underestimating them.
“If PSV were that good, they should have won it big but they didn’t. They did dominate but created very little.
“Rangers can wait as long until you made a mistake.”
Rangers are going into the game on the back of a 2-0 away win away at Ross County at the weekend.
