The former AC Milan playmaker watched his old side struggle against Neil Lennon's Scottish champions at home last week yet still emerge with a 2-0 win.
Gullit - who was speaking at Gleneagles as he promoted next year's Ryder Cup - said: "I saw the Milan game, Celtic had unbelievable opportunities to score goals but they didn't do it, because of quality.
"Any little chance Milan get, they will score. That's the reality of being in such a big competition.
"Celtic in Scotland get loads of chances to score and if they miss one that's okay, but not in Italy."
Gullit also starred for Feyenoord and PSV and has extensive knowledge of Celtic's other Group H rivals, Ajax, and insists the double-headers on October 22 and November 6 will be pivotal to both teams' hopes of qualification for the last 16.
Frank de Boer's side has shipped eight goals in two defeats to Barcelona and then domestic rivals PSV Eindhoven in the past week and Gullit said: "Ajax have proved to do well against British teams recently so it's going to be interesting.
"The matches with Celtic will be even I think - they play different styles of football but that's good so I'm looking forward to those games."