The Blues were drawn with Schalke 04, Sporting Lisbon and FK Maribor in their European group, meaning they avoided many of the continent's bigger sides.
But Mourinho is wary of complacency creeping in at the west London side and has highlighted the strengths of the three teams Chelsea will face.
"On paper... but, at the end of the day, we play against a German team [Schalke]. Germans are German... world champions, good league, good teams, strong guys," he told reporters ahead of his side's clash with Everton.
"The Portuguese team [Sporting Lisbon] I respect a lot - and not because I'm Portuguese. It's because I know them well and, if the league is not a very strong, the three big teams are big teams.
"They have potential, history and status and they play without fear. And Maribor brings the danger of 'the new guys.' They have nothing to lose, everything to win."
Meanwhile, the 'Special One' also fielded questions on Romelu Lukaku, the ex-Chelsea striker who signed for Everton in a £28 million deal this summer.
The Belgian target man spent last season on loan at Goodison Park and Mourinho insists the most important thing for the forward is that he now happy where he is.
"I think he's happy and that's the most important thing. He wants to be very important, a first-choice player all the time," the 51-year-old mused.
"He connected well last season [at Everton], with the manager, with the fans. He's happy, has a big career in front of him. He's happy - that's the most important thing."
On the subject of Lukaku, Chelsea full-back Cesar Azpilicueta also sounded a warning to his team-mates:
“We all know Romelu. He is a very good player and has signed for Everton," he said.
“He was happy there [on loan] last season and we know he is going to be a threat because he’s a very dangerous striker.”