Arsenal were drawn on Friday to play Fenerbahce in the Champions League playoffs as they seek a 16th straight season in the lucrative group stage.
However, a pending match-fixing case involving Fenerbahce at sport's highest court means the Turkish club could be expelled from the competition even if they win.
Seven-time winners AC Milan were paired in the draw with PSV Eindhoven, the 1988 European champion, with the first match in the Netherlands.
"It's a classic European cup match-up,'' Milan director Umberto Gandini told The Associated Press.
"It's a pleasure to play with such a historical club, and it's a difficult task.''
Olympique Lyonnais v Real Sociedad
Schalke 04 v Metalist Kharkiv
Pacos de Ferreira v Zenit St Petersburg
PSV Eindhoven v AC Milan
Fenerbahce v Arsenal
Steaua Bucharest v Legia Warsaw
Dinamo Zagreb v Austria Vienna
Viktoria Plzen v Maribor
Ludogorets Razgrad v FC Basel
Shakhter Karangandy v Celtic
First-named team to play first leg at home. First legs to be played on Aug 20 or 21, second legs on Aug 27 or 28.
Schalke were drawn to play Metalist Kharkiv, who are also threatened with UEFA sanctions for a years-old domestic match-fixing case. The Ukrainian club faces a disciplinary hearing at UEFA on Tuesday.
Among the 10 pairings it was: Lyon vs. Real Sociedad, Pacos de Ferreira vs. Zenit St. Petersburg and newcomer Shakhter Karagandy hosting Celtic. The Scottish champions face a long trek to Kazakhstan for the first match.
First legs are played August 20 or 21 and return matches on August 27 or 28.
Winners advance to the elite 32-team group stage - joining established powers like defending champion Bayern Munich, Barcelona, Real Madrid and Manchester United - which will be drawn August 29 in Monaco.
The Court of Arbitration for Sport has set an August 28 deadline to rule on Fenerbahce's appeal against a two-year ban from UEFA competitions. No hearing date has been set.
UEFA's Champions League rules require clubs not to have been involved in fixing matches since April 2007, and several Fenerbahce officials were convicted in a criminal trial of fixing matches during the club's 2011 national title run. They deny wrongdoing.
Metalist also faces UEFA sanctions after CAS last month dismissed an appeal by the Ukrainian club's sports director against a five-year ban from football. The Ukrainian federation had judged that Metalist's 4-0 win against Karpaty Lviv in an April 2008 league match was fixed.
Metalist vice president Konstantin Pivovarov confirmed that, even if UEFA rules against the club, it is likely to appeal that verdict at CAS and try to continue in the competition.
"We're expecting to play Metalist,'' Schalke official Moritz Beckers-Schwarz said.
If Metalist are removed, their defeated third qualifying round opponent - PAOK Thessaloniki, led by a former Schalke coach - could in theory be reinstated.
"We would like to play PAOK because Huub Stevens is the coach now and that would be an interesting issue,'' Beckers-Schwarz said.