The winners advance to a play-off round when a further 41 teams enter.
That stage will include losing teams from the Champions League third qualifying round, plus domestic cup winners and other teams from Europe's strongest football nations.
A tournament format will see 48 teams play in 12 four-team groups between September and December before a knockout stage begins next February featuring additional teams from the Champions League group stage.
The final is scheduled to be played in Hamburg on 12 May.
Europa League third round qualifying ties involving British & Irish clubs:
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