Even by European Champions League standards, the stakes will be dramatically high for Fenerbahce and Arsenal in a playoff round first-leg clash on Wednesday.
Arsenal seem to be in turmoil after an English Premier League opening day loss fuelled fans' fury at the cash-rich club's failure to sign big-name offseason targets.
"I believe our season will depend on how we respond to this defeat,'' Arsenal manager Arsene Wenger said Saturday after a 3-1 loss to Aston Villa on Saturday provoked hostile boos at the Emirates Stadium.
Fenerbahce, who also lost their league opener, play while appealing their expulsion by Champions League organiser UEFA in a long-running domestic match-fixing case.
The Court of Arbitration for Sport could yet decide, in a ruling expected after the return match in London next week, which team advances to the lucrative group stage and collects $20-$33m in UEFA prize money.
Tuesday 20 August
S Karagandy v Celtic
Lyon v Real Sociedad
Pacos Ferreira v Zenit St P
Plzen v NK Maribor
PSV Eindhoven v AC Milan
Wednesday 21 August
Din Zagreb v Aust Vienna
Fenerbahce v Arsenal
Ludogorets R v FC Basel
Schalke 04 v Paok Salonika
S Buch’t v Legia Warsaw
Like Arsenal, AC Milan regards a place in the Champions League group stage as key to their image and finances.
The seven-time European champions begin their season Tuesday away to PSV Eindhoven, the 1988 European Cup winner that already reeled off three wins to sit atop the Dutch league.
Zenit St. Petersburg offer a tricky debut for Champions League newcomer Pacos de Ferreira, who host the first leg in Portugal on Tuesday.
Also on Tuesday, Celtic have made the six hour-plus flight to face Kazakhstan champions Shakhter Karagandy; Lyon hosts Real Sociedad and Viktoria Plzen hosts Maribor.
Wednesday's five-match line-up includes: Dinamo Zagreb vs. Austria Vienna, Steaua Bucharest vs. Legia Warsaw and Ludogorets Razgrad vs. Basel.
Schalke host PAOK Thessaloniki, who were reinstated by UEFA last week.
PAOK previously lost to Metalist Kharkiv, who were later expelled when a 2008 match-fixing case was resolved this month.
Three of the 10 playoff pairings have been affected by UEFA match-fixing investigations since current champion Bayern Munich beat German rival Borussia Dortmund at Wembley Stadium in May.
Fenerbahce's case has the greatest potential for drama, even after the return matches conclude next week.
The Istanbul club, UEFA and CAS could not process their challenge to a two-season ban from European competitions before the matches against Arsenal.
During an offseason legal saga, Fenerbahce forward Dirk Kuyt wrote to UEFA on behalf of the players. Kuyt said they had "a lot of questions'' about the punishment dating back to allegedly fixed matches in the 2010-11 Turkish season.
"This is not even proven that we are guilty'' wrote Kuyt, whose club president was among several officials convicted in a criminal trial. They deny wrongdoing and have appealed.
Injury-hit Arsenal know they could lose over two legs and still get a 16th straight season in the group stage - though Salzburg, Fenerbahce's beaten opponent in the previous qualifying round, could also seek reinstatement.
England winger Alex Oxlade-Chamberlain is the latest Gunners casualty, sustaining a serious knee injury Saturday to join defenders Thomas Vermaelen and Nacho Monreal, plus midfielders Mikel Arteta and Abou Diaby on the sidelines.
Milan, who began in Serie A at Verona on Saturday, have played only friendlies ahead of facing match-fit PSV, now coached by former Netherlands midfielder Phillip Cocu.
Schalke lost Dutch forward Klaas-Jan Huntelaar to a knee ligament injury in their 4-0 loss at Wolfsburg on Saturday.
The revised fixture with PAOK brings the Greek club's coach Huub Stevens back to Schalke where he won the UEFA Cup in 1997, and a second spell in charge ended last December.
Romanian champions Steaua, the 1986 European Cup winner, host Legia while club President Gigi Becali serves prison time for financial wrongdoing.
In June, UEFA weighed allegations that Becali tried to pay bribes to influence a 2008 league match, and deferred Steaua's one-year suspension for a five-year probation period.
The 10 playoff winners join 22 elite teams that qualified directly for the lucrative group stage. The draw is made August 29 in Monaco.