José Mourinho has called on Chelsea to secure their passage into the knockout phase of the Champions League with victory at Basel on Tuesday as his players enter a cluttered and pivotal period of the season where "only the brave can survive".

A victory at St Jakob-Park will claim Group E for the Europa League holders and allow Mourinho to rest key personnel for the final group game against Steaua Bucharest. Chelsea have nine fixtures in all competitions in December with Mourinho, sporting a repeat of his self-styled "going to war" crewcut from 2006, urging his players to prove their quality and stamp their authority on the campaign.

"This is a period I like, a period where the squad can play a role, not just the team," the manager said. "It's a period where I think only the brave can survive because it's so hard. We go into the Christmas period and the accumulation of matches is so high. We don't do it as a normal thing … we do it as a special group with a special mentality, enjoying the situation and forgetting we don't have a Christmas like the Spanish, Italian and German players. But we have the pleasure of playing a period that's only for the brave.

"I always enjoyed this part of the year when I was in England, and I missed it when I was in Spain and Italy. We need a special mentality to cope with that situation. Nine matches, and one of them is the match against Steaua. Finish the job against Basel and we would ensure that, instead of having nine competitive matches, we only have eight. That would be important. That's our motivation, to kill the situation in the group stage and give us a bit of space in December."

Mourinho, who has Fernando Torres available again after a groin injury but has lost David Luiz to a bruised knee, admitted he had cut his own hair at the training ground last week while all but four of his players were absent on international duty. The savagely cropped style is similar to that sported seven years ago when he had embarked on his third and ultimately tempestuous campaign at the club by declaring: "Look at my haircut – I am ready for war."

This time the crop may more have reflected the tedium of the international window, even if he had felt compelled to send a selfie to his wife before venturing back home. "I did it myself down at the training ground," he said. "I asked Fernando to give me his machine [clippers], and I did it myself in front of the mirror. It's nice and cheap. Some people can't do what I did. In a couple of months, I'll have hair again. Some other people wouldn't … I did send a picture of it to my wife before I arrived home to see if I'd be allowed in, and yes, there was no problem."

The desire to win the group should see Torres restored having missed three club matches with a groin injury sustained in training, though Juan Mata may once again be left stewing on the bench despite his manager praising his professionalism on the fringes. "That's a consequence of the squad we have because Juan deserves to play given the way he works and behaves," he added. "It's hard for them when they're not playing, and it's hard for me. I don't have a special pleasure leaving players out. I enjoy playing them and making them happy, but there's nothing I can do."

Basel, top of the Swiss league and unbeaten domestically since mid-August, won the group's opening fixture at Stamford Bridge only to struggle in the months since. There was an admission from their midfielder, Fabian Frei, that they would welcome even a point against the Londoners with one eye on securing Europa League qualification.

"If somebody tomorrow has to feel the pressure, it's not us," Mourinho said. "It's Basel because they are in a limited situation to qualify for the next round. This is a difficult game, but this Chelsea is better than the Chelsea that played at Stamford Bridge. Hopefully we can continue the good run we've had in the Champions League and finish the job."