Celtic will meet Slavia Prague if they reach the Champions League play-offs, Ajax perhaps have an easier draw, and Porto face a big test.
Ajax will meet either APOEL or Qarabag in the Champions League play-offs if they defeat PAOK in the third qualifying round.
Last season's semi-finalists will take on the champions of Cyprus or Azerbaijan in a two-legged tie if they overcome the 2018-19 Greek Super League winners.
Scottish champions Celtic will take on Slavia Prague if they make it through their third-round tie with CFR Cluj.
Porto or Krasnodar will face Istanbul Basaksehir or Olympiacos, while Basel or LASK will meet Club Brugge or Dynamo Kiev.
Swiss champions Young Boys await Red Star Belgrade or Copenhagen, and Dinamo Zagreb or Ferencvaros will play Maribor or Rosenborg.
The first legs of the third-round matches are on Tuesday and Wednesday, with the return games on August 13.
The play-off matches take place on August 20-21 and August 27-28.
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