Awayday tests for Chelsea, Manchester United
Despite their status as defending champions, Chelsea cannot be complacent having already dropped two home points to Juventus, though they should make good the shortfall with success at Danish Group E minnows Nordsjaelland.
Juve fans, meanwhile, will expect to see their side, who came back from 2-0 down in London, sit atop the group come Tuesday night after tackling Shakhtar Donetsk in Turin.
In contrast, while Chelsea rule at home but have ground to make up in Europe after Donetsk pocketed an expected win over Nordsjaelland in their opener, the boot is on the other foot for Manchester United.
Alex Ferguson's side may have done the minimum expected of them in dispatching Turkey's Galatasaray in their Group H opener at Old Trafford.
But two defeats in six league games -- including a first home loss to Tottenham in 23 years on Saturday -- have left the three-time European champions four points off the pace in the league and dented confidence ahead of their trip to Romania's Cluj.
Cluj coach Ioan Andone will be feeling it could just be third time lucky for him as he locks horns with Ferguson for the third time in his career.
Andone was in charge at Dinamo Bucharest when United beat them in a 2004-05 qualifying tie and he also turned out for his country 26 years ago when Scotland, then briefly managed by Ferguson, ran out 3-0 winners in a friendly international.
Having exited at the group stage last season United will not make the mistake of underestimating the Romanians, who have already banked three away points following their success at Portugal's Braga.
French veteran defender Patrice Evra says United have to shrug off the Tottenham reverse quickly.
"We have to be positive. It's not a bad start to the season," said Evra.
"I hope it was just an accident and we can get back the winning mentality in the Champions League and against Newcastle (next weekend)."
As United look to move on there is nothing but optimism in the air at Chelsea. Not only are they top of the Premier League but the signs are that Fernando Torres is finally fitting into the Stamford Bridge jigsaw.
Dogged by poor form since his Â£50 million switch from Liverpool, and overshadowed by former teammate and Champions League final goalscorer Didier Drogba, the Spaniard bagged the opening goal at Arsenal and freely admits the clouds are lifting for him.
"I am enjoying it more this season with the kind of players I have in the middle behind me," Torres told Chelsea.tv, adding he and the team are changing their style.
"With this different style of football we are playing this season we are at the top of the league and can dream of a very good season again," said the striker.
"I had a very difficult beginning at Chelsea but that is in the past now, and I am enjoying the present with a great group of players and we are building a big team."
Elsewhere, Bayern Munich, who extended their perfect record in the Bundesliga on Saturday by beating Bremen, can add to an opening success over Valencia in Group F if they defeat BATE Borisov in Belarus.
Even so, sporting director Matthias Sammer told the four-time European champions they have room to improve as against Bremen "we weren't totally awake and didn't reach our full potential."
Valencia must play catch-up at home to likewise pointless Lille.
Neutrals will have an eye on Barcelona's progress in Lisbon against a Benfica side held by Celtic in their first match while the Scots face a tricky test at Spartak Moscow.
Spartak were only denied victory in the Nou Camp by a pair of late goals from the peerless Lional Messi, whom Benfica must somehow keep quiet at the Estadio da Luz.
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