Chelsea are top of Champions League Group E, just ahead of second-placed Schalke, with both teams taking six points from their opening three matches.
And the Chelsea manager says he will leave nothing to chance as he prepares for the visit of the German side on Wednesday night.
Mourinho said: "I don't know what they want from the group phase, if they are going to try everything to finish first or if they are going just to try to finish second and progress in the Champions League.
"I have to prepare my team for both situations. But, for sure, they are a difficult opponent and the result in Germany, 0-3, means nothing."
Mourinho also revealed he was far from impressed with his team's performance in their last Premier League match as they suffered a 2-0 defeat at St James' Park.
"The problem for me was just the attitude," he said. "I expect my team to be much more than it was against Newcastle.
"I was frustrated because I want my team to be always active and proactive and not reactive and not waiting for things to happen.
"And I just simply didn't like (it). I want better from my team."
Chelsea will have to make do without Fernando Torres for Wednesday's match at Stamford Bridge after the Spain international was ruled out with a leg injury.
Gary Cahill, an unused substitute for the loss against Newcastle, is confident Chelsea can cope without the absent Torres and believes they will put in a much-improved performance against Schalke.
"The onus will be on us, being at home, to be on the front foot," Cahill said.
"We're at Stamford Bridge and if we go out with the same attitude as in the away leg, I'm sure we'll be OK.
"As players, you want to get straight back out there and put things right. It gives us the opportunity to do that."
Chelsea v Schalke is on Sky Sports 2 on Wednesday night from 7.30pm