London :Barcelona's reign as Champions Cup holder could be over as early as on Tuesday if the Spanish club loses at home to Inter Milan and group rival Rubin Kazan beats Dynamo Kiev.
What may have seemed unthinkable when the draw was made in August is now a reality for coach Pep Guardiola and his talented side. And the fact that Lionel Messi was one of six players who missed training on Sunday added to Guardiola's woes as he faces up to a tough game against the Italian champion.
An attack of swine flu has already ruled out defender Eric Abidal and midfielder Yaya Toure, and Rafael Marquez is awaiting tests to see if he has become the third victim.
Strikers Messi and Zlatan Ibrahimovic have leg injuries and defender Gerard Pique could only do light training in the gym.
"We have no other option than winning. And we hope the fans respond," midfielder Sergio Busquets said. "The players will be giving it 200 percent, and know that with the fans behind them, they will be stronger still.
"Whoever is available to play will be looking to get through this with all the enthusiasm we have."
Inter's 3-1 victory at Bologna on Saturday strengthened its healthy lead atop the Serie A standings, making Jose Mourinho's team more confident about capturing a place in the last 16 in the European competition with a victory at Camp Nou.
Barcelona goes into the game in third place in the group with five points, one behind Inter. Rubin, which captured its second consecutive Russian league title Saturday, also has five points and can make it eight when it hosts last place Kiev.
Even if Barca finishes level on points with Rubin after the last round of qualifying, the head-to-head record _ Rubin won in Barcelona and played a scoreless draw in Kazan _ would give the Russian club the edge.
Barcelona is not the only European heavyweight in danger of going out this week.
Five-time winner Liverpool is on the verge of elimination with five points to make up on second place Fiorentina. Lyon is already out of reach.
Rafa Benitez' team goes to Hungary to face Debrecen and even a victory won't be enough if Fiorentina beats Lyon at home.
Liverpool's own form _ one win in 10 games in all competitions _ doesn't suggest a recovery, especially with top striker Fernando Torres out of the lineup because of a lingering groin problem and two more players picking up injuries in Saturday's 2-2 draw at home to Manchester City in the Premier League.
AC Milan and Real Madrid, who have a combined 16 title triumphs in European football's biggest competition, are level on on seven points ahead of Wednesday's Group C games.
Milan hosts Marseille, which is third with six points. Spanish league leader Madrid, which has won the European title nine times but not since 2002, should be confident of beating last place FC Zurich at home.
Six teams, including two from England and two from France, already have secured spots in the last 16 with two games to spare. They are Manchester United, Chelsea, Bordeaux, Lyon, FC Porto and Sevilla and their aim now is to try and finish group winners, which would mean facing a runner-up in the knockout round.
With Bordeaux already through, two more former European champions are vying for the other spot from Group A, with Bayern Munich needing to make up four points on second place Juventus.
Bayern coach Louis van Gaal's job is already in danger ahead of a home match against Maccabi Haifa, while Juventus can qualify with a victory at Bordeaux.
Arsenal needs only a point at home to third place Standard Liege on Tuesday to reach the last 16 and a victory at the Emirates Stadium will guarantee the Gunners finish top of Group H.
Four points behind, Olympiakos holds second place and travels to last place AZ Alkmaar.
In Group G, second-place Unirea hosts group leading Sevilla, while third place Stuttgart visits Rangers.
With Man. United already guaranteed a place in the last 16, CSKA Moscow and German champion Wolfsburg are fighting over the other place from Group B and meet in Russia on Wednesday.
A Wolfsburg victory will guarantee a place in the second round.