@Cerval
You've misheard.
Winners: Juventus
• Juventus have already qualified for the group stage via their domestic league, thereby would create a vacancy in the group stage.
• To fill that vacancy, the UEFA Europa League winners would definitely enter the group stage.
• The third-placed Italian side would enter the play-offs, league route in accordance with the 2017/18 access list.

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See Real Madrid make it to Cardiff
Winners: Real Madrid
• Real Madrid have already qualified for the group stage via their domestic league, thereby would create a vacancy in the group stage.
• To fill that vacancy, the UEFA Europa League winners would definitely enter the group stage.
• The fourth-placed Spanish side would enter the play-offs, league route in accordance with the 2017/18 access list.
Basically, united are in group stages, irregardless of who wins in cardiff.
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