Chelsea's chances of successfully defending their Champions League crown will be given a stiff early examination when they take on Italian champions Juventus at Stamford Bridge on Wednesday.

Chelsea defender John Terry (C) during a team training session in London on September 18 

Roberto Di Matteo's men will host the Serie A title-holders four months to the day after winning the trophy in a dramatic penalty shoot-out against Bayern Munich in the Allianz Arena, and they would appear to come into the Group E game in great nick.

However, Di Matteo knows the rest of the continent will up their game every time they play the defending champions.

"Every opposition is going to play with extra motivation playing against the holders of the Champions League. So it makes our lives more difficult," said the Italian.

"I'm aware no team has defended the trophy and I'm not surprised because it's such a difficult competition to win.

"To win it twice in a row has proven impossible so far, because it's so competitive."

Juve are making their first appearance in the competition in three years, but they have not lost a Serie A game since the start of last season.

Chelsea, who could only manage a goalless draw at local rivals Queens Park Rangers in the Premier League on Saturday, should be able to call on the services of John Terry despite the England defender suffering a knee injury at Loftus Road.

In addition, Juan Mata trained at the weekend and was hoping to return to full fitness in time to feature.

The other English club in action on Wednesday are Manchester United, who are desperate to put their shock group-stage exit of last season behind them.

The Red Devils entertain old foes Galatasaray, who famously knocked them out of the competition in 1993, and Sir Alex Ferguson has vowed not to repeat the mistakes that cost his side dear 12 months ago.

"If we don't go through, we will be criticised and pilloried for it and quite rightly," said Ferguson, who is expected to field his strongest starting line-up for the Group H encounter, including Robin van Persie and Shinji Kagawa.

"We've had our warning and I don't anticipate going out this time.

"We've had opportunities in the competition. We've lost two finals to Barcelona and won two in the last decade or so but we want to do better. Certainly, we'll do better than last year - no question about that."

Fresh from winning their first four Liga games under Tito Vilanova, Barcelona play host to Spartak Moscow at the Camp Nou in their Group G opener.

The Catalans will be without the physical presence of skipper Carles Puyol, who has been ruled out for at least a month after suffering a knee injury in the 4-1 weekend win at Getafe.

Juventus midfielder Andrea Pirlo (L) during a team training session in London on September 18 

However, they are heavy favourites to beat the Russians, who are now coached by Spanish former Valencia boss Unai Emery but have struggled for consistency in the early weeks of their domestic season.

In the other game in Group G, Celtic make their return to the competition after a four-year absence with a home clash against Benfica in Glasgow.

Despite a relative lack of experience in their squad, and some questionable domestic form of late, goalkeeper Fraser Forster believes the Scottish champions have reason to be optimistic.

"The quality of the players we face will be a big step up but we just have to go out and do our best and hopefully that will help the squad develop and move forward," he said.

Last season's runners-up Bayern begin their latest bid for a fifth European Cup with a home clash against Valencia in Germany, and it's a game that skipper Philipp Lahm will not be taking lightly by any means.

"Wednesday will be a proper test," he told Bayern's official website. "Valencia are a top team, they're almost always in the Champions League, and almost always one of the best three clubs in Spain."

Bayern and Valencia are in Group F along with Lille and BATE Borisov, who clash in France.

Elsewhere, Ukraine's Shakhtar Donetsk play Danish champions Nordsjaelland in Group E, while Braga and CFR Cluj meet in Group H.