A clearer picture of the likely qualifiers for the knockout phase of the Champions League should emerge as the group stage reaches its halfway point this week.

Clearly, with only two of the six matches completed so far, no team is certain of qualifying and none are eliminated, but results on Tuesday and Wednesday will have a big bearing on both of those issues.

Chelsea (Group A), Bayern Munich (Group B), Valencia (Group D), Olympique Lyon (Group E), Manchester United [Images] (Group F) and Arsenal [Images] (Group G) have won their opening two matches and victory this week would more or less guarantee they advance to the last 16.

Chelsea host Barcelona, Bayern travel to Sporting Lisbon, Valencia take on Shakhtar Donetsk, Lyon go to Dynamo Kiev, Manchester United host FC Copenhagen and Arsenal travel to CSKA Moscow [Images].

In contrast, Levski Sofia (Group A), Inter Milan (Group B), Dynamo Kiev (Group E) and Hamburg SV (Group G) cannot afford another defeat -- or else the best they would probably be looking at is a consolation place in the UEFA [Images] Cup.

Levski travel to Werder Bremen, who went top of the Bundesliga at the weekend with a 6-0 win at Bochum, Inter are at home to Spartak Moscow, Kiev host Arsenal and Hamburg SV travel to Porto.

BIG MATCH

The outstanding match of the week takes place in London [Images] where Chelsea meet title holders Barcelona for the third successive Champions League campaign.

Chelsea knocked Barcelona out of the competition two seasons ago, Barcelona knocked Chelsea out last season, but the edge has been taken off this meeting a little because they are meeting in the group stage.

With Werder and Levski completing the group, Chelsea and Barca should advance whatever happens in the two matches between them, but neither will want to lose on Wednesday.

Chelsea could be disadvantaged by being without either first choice goalkeeper Peter Cech or his deputy Carlo Cudicini after both were injured and taken to hospital on Saturday during Chelsea's 1-0 win at Reading.

Cech is definitely out after undergoing surgery for a depressed fracture of the skull on Saturday night, while Cudicini was discharged from hospital after being knocked unconscious late in the game.

Chelsea's third-choice keeper, the 31-year-old Portuguese Hilario, could make his first team debut against Barca.

DARK HORSES

In the same group, newcomers Levski, still searching for their first point, hope to give Werder a good run for their money.

The 24-times Bulgarian champions lost 5-0 to Barcelona and 3-1 to Chelsea but are desperate to capture the third place in the group which will be their ticket to the UEFA Cup.

Even before the season began, Lyon were being spoken of as a dark horse that could wrest the crown from Barca and the French champions look too good on paper for Dynamo Kiev.

The Group E leaders travel to face the bottom-of-the-table side after overcoming a tough domestic challenge from their arch-rivals St Etienne to snatch a 2-1 home victory thanks to a last-minute strike by playmaker Juninho.

Lyon have won nine successive matches in all competitions and could make that 10 in Ukraine.

"A win is always the best way to prepare for a Champions League match," said coach Gerard Houllier.

"But we must be wary of Kiev as they will have nothing to lose. They lost to Bucharest and Real Madrid [Images] and they will be out for a do-or-die game."

Lyon will be without their French international goalkeeper Gregory Coupet who picked a hand injury last week. He will be replaced by Remy Vercoutre.

Swiss central defender Patrick Mueller is also out following a shoulder injury sustained during last week's friendly international against Austria.

HUGE RELIEF

Striker Fred, suspended for the derby against St Etienne on Saturday, is back in action.

Another top versus bottom clash sees Girondins Bordeaux take on Houllier's old club Liverpool, who are top of Group C.

Bordeaux struggled to tame lowly Monaco 1-0 at home on Saturday while Liverpool did not play all that well in a 1-1 draw at home against Blackburn Rovers.

But the win over Monaco was a huge relief for Bordeaux after two consecutive defeats, including a 1-0 loss to PSV Eindhoven which left them bottom of Group C.

Bordeaux have still to score a goal in the competition but will have to do so without Czech midfielder Vladimir Smicer, who was in the Liverpool team that won the European Cup 17 months ago.