Celtic defender Kristoffer Ajer believes Cluj sent a recent reminder of their danger ahead of Thursday night's Europa League encounter.
The Hoops were knocked out of the Champions League qualifiers on aggregate by Dan Petrescu's side on August 13, following a 4-3 home defeat.
Cluj were themselves dismissed in the play-off by Slavia Prague and were then drawn in Group E of the Europa League along with the Scottish champions.
And on the same night Celtic began their campaign with a 1-1 draw against Rennes in France, Cluj beat Italian side Lazio 2-1 in Romania.
Ahead of match-day two at Parkhead, the 21-year-old Norway defender said: "Obviously we want to do better than we did the last time at Celtic Park.
"We know it is a massive game for us and we also know that Cluj will make it really difficult for us.
"They showed in the first game against Lazio that they are a top, top side and we will have to be at our very best to get points.
"I wasn't surprised. Romania is a really tough place to go so for them to get that result at home just shows that every team in this group can take points off you so you have to be focused and ready for everything.
"We have a great chance to go through this group and that is our main target.
"We have the Celtic mentality of taking one game at a time and we have to look after tomorrow evening."