Schalke coach Jens Keller is wary of the threat a confident Steaua Bucharest side will pose his team on Wednesday.
The Romanians have reached the UEFA Champions League group stages after coming through qualifying, eliminating Vardar, Dinamo Tbilisi and Legia Warsaw on their way into Group E.
Schalke have made a slow start in the Bundesliga and sit ninth despite winning their past two league matches.
And an in-form Steaua, who are unbeaten in 12 competitive games this season, have Keller worried.
"It is going to be a tough game. Physically they are extremely strong and they have a lot of self-confidence right now," Keller said.
"They won all their games and are in the group stage now. So we are aware it is going to be tough game tomorrow at home.
"But I also always said that we have done really well the last few weeks. We built up confidence and we want to win this game."
Schalke have been given a boost ahead of the clash, with defenders Christian Fuchs and Felipe Santana set to return from injury.
Tim Hoogland is the only player unavailable from the Schalke squad, which overcame Mainz 1-0 in the league on Saturday.
"Christian Fuchs and Felipe Santana will be back. They are both fit again," Keller said.
"Jermaine Jones is still suspended and the only one that can't play after the weekend is Tim Hoogland who has some problems with his pancreas - I think, please don't hold me to that."