Chelsea's bid to win a third major European trophy in successive seasons begins when they host Basel in the Champions League.
The Premier League side won the Europa League last season, while they lifted the Champions League in the 2011-12 campaign, and they will be determined to claim the main prize again.Chelsea and Basel are well acquainted, having met in the semi-finals of the Europa League last term, with the Blues winning 5-2 on aggregate.
That success came under interim manager Rafael Benitez, though, with Mourinho in charge now as he looks to win the title for the third time.
The Portuguese has won the Champions League at both Porto and Inter but is yet to win it at Chelsea, coming closest in 2004-05 and 2006-07, when they reached the semi-finals.
The Londoners have not made an ideal start to the season, winning just two of their first four Premier League matches, while they lost to Bayern Munich in the Super Cup final on penalties in August.
As a result, they lie sixth in the Premier League table, with Saturday's 1-0 defeat at Everton fresh in the memory.
Cameroon international Samuel Eto'o made his debut in that fixture but the 32-year-old striker was guilty of missing several chances.
Mourinho will expect more from the former Inter player and Spaniard Fernando Torres may start as a result of his sub-standard performance.
Chelsea's array of young stars could all play big roles in the Champions League this season, with Oscar, Eden Hazard and Andre Schurrle all impressing in the early stages of the campaign.
Basel have their own stars to boast and among those is veteran forward Marco Streller, who has already racked up four goals in just five games in the Swiss Super League.
Their league form has been good, losing just one of their seven matches this season, and they sit third on the table as a result.
The Swiss side have form for giant-killing - they essentially knocked Manchester United out of the group stages in the 2011-12 Champions League by beating them on the last matchday of the group stages - and Murat Yakin's side have had to work hard for their spot in this year's competition.
They beat Maccabi Tel Aviv 4-3 on aggregate before toppling Ludogorets 6-2 in the play-off round.