The "it" that Mourinho referred to was his team's 2-1 defeat to Swiss outfit FC Basel at Stamford Bridge on matchday one of the Champions League earlier this month.

So, ahead of Chelsea's must-win fixture, what is there to know about Steaua Bucuresti? Read on...

History

Founded in 1947, capital-based Steaua quickly established themselves as one of Romania's most successful clubs. However, following a trophy-laden spell throughout the 1950s, the Red and Blues struggled for league titles (winning just three) during the 1970s and much of the 1980s. Instead, they had to settle for numerous successes in the domestic cup.

Steaua Bucuresti players celebrate their win over Ajax in February 2013. © Getty Images

However, in 1986 they enjoyed their finest hour to date, becoming the first Romanian side to win the European Cup. They held Spanish giants Barcelona to a 0-0 draw in the final, before Helmuth Duckadam saved four penalties in the shootout to secure the famous trophy.

Steaua's league success earlier this year means that they have won Liga I on 24 occasions, while they have finished runners-up a further 13 times. Add to that 21 Cupa Romaniei triumphs, and it is clear to see why they are Romania's most popular club side.

Notable former players

Chelsea fans will remember Dan Petrescu, who during his five-year stint in West London won the FA Cup and League Cup. The full-back, who now manages Russian side Dynamo Moscow, started his career with Steaua, amassing over 100 appearances for the club before he moved to Italy.

The club's connection with the army also saw Gheorghe Hagi spend three years with them before he transferred to Real Madrid.

Dan Petrescu gives out orders to his Dynamo Moscow players in July 2013. © Getty Images

Tottenham Hotspur also profited from Steaua earlier this year when they signed centre-back Vlad Chiriches.

Players to watch out for

Federico Piovaccari: The Sampdoria loanee has impressed since joining Steaua in July this year. The 29-year-old has scored seven goals to date, including three during the qualification process for this term's Champions League group stages.

Adrian Popa: The current Romania international, who wears the number 77 shirt, operates on the right flank. Although primarily in the team to create opportunities for the likes of Piovaccari, Popa has found the net three times himself this season.

Stadium

The Arena Nationala is Romania's biggest football ground, which played host to Athletic Bilbao and Atletico Madrid for the 2012 Europa League final. It has a capacity of 55,611, although Steaua matches rarely attract close to that mark. The two-year-old facility, where the Red Hot Chili Peppers and Depeche Mode have performed, has a retractable roof that takes 15 minutes to fully close.

Previous meetings

These teams will know each other well, having met in the Europa League last season. Steaua won the first leg in Romania 1-0 thanks to Raul Rusescu's penalty, but Juan Mata levelled up the score on aggregate in the return leg at Stamford Bridge. Chiriches then put the visitors back in command, but late goals from skipper John Terry and Fernando Torres saw the Blues advance.

Steaua were also involved in one of the UEFA Cup's most memorable matches back in 2006 when they took on Middlesbrough. Leading 1-0 from the opening leg, the Romanians were soon 3-0 up on aggregate at the Riverside Stadium. However, a late goal from Massimo Maccarone secured a 4-3 overall win for Boro, who advanced through to the final.

Of the eight matches that Steaua have played against English clubs at home, they've won five of them, losing just once - that was to Arsenal in 2007 when Robin van Persie scored the only goal of the game.