Jose Mourinho turns attentions to Europe knowing Chelsea can't afford defeat to Steaua Bucharest on Tuesday

The Portuguese claims his side must improve if they are to remain in the competition even at this early stage

Jose Mourinho knows his Chelsea side have little margin for error in the Champions League ahead of their second Group E contest at Steaua Bucharest on Tuesday night.

Defeat for the 2012 European club champions against Basle in the opening round came as a shock as Chelsea were anticipated to pass through a pool also containing Schalke at a canter.

That expectation was not due to Chelsea's last foray in the Champions League - in 2012/13 the Blues became the first holders to exit the competition at the group stages - and owed more to the presence of Mourinho.

After the Basle blow, the Blues are playing catch-up, with Mourinho targeting 12 points to advance to the knockout stages, with a victory in Romania the initial objective.

"We cannot lose and probably we have to win," Mourinho said. "With 12 points you qualify. It's very difficult that you don't qualify with 12 points. Probably less.

"We still have 15 points to fight for. We still have space to make a mistake.

"But when you make a mistake in the first game, you don't want to make a mistake in the second too. If you do, you are in trouble."

Mourinho knows winning the opening two fixtures is not essential in the tournament, as his Inter Milan team drew three before winning in round four and going on to lift the Champions League trophy in 2010.

But he would prefer not to have to do things the hard way as Chelsea seek a second away win this season.

The Blues have played Manchester United, Bayern Munich, Everton, Swindon and Tottenham away from home, with their only success coming against League One opposition at the County Ground in the Capital One Cup.

Mourinho hopes that will change to get his side's Champions League campaign back on track.

Steaua, who lost 3-0 to Germany's Schalke in the first round, provide familiar opposition for Chelsea, if not Mourinho.

Under interim boss Rafael Benitez, Chelsea lost to Laurentiu Reghecampf's side at a National Arena pulsating with partisan support.

Following the Europa League last-16 first leg loss in Bucharest, the Blues bounced back at home, winning 3-1 to advance 3-2 on aggregate and they eventually won the competition.

Mourinho has been scathing about the Europa League, insisting the Champions League is the only competition for Chelsea.

And he knows his side must make amends for their defeat to Swiss side Basle, another beaten in the Europa League last term, if they are to avoid the possibility of falling into the second-tier competition this term.

Mourinho added: "We have to try to go to Bucharest and to win to try to make a little balance with the three points we lost at home."

PA