Cristiano Ronaldo could miss an expected return to Old Trafford with Juventus after being sent off for the first time in his Champions League career.
The Portuguese was making his first appearance for Juventus in the competition but saw red in the 29th minute of the 2-0 Group H win over Valencia for an off-the-ball incident in the penalty area.
A main focus of the draw was Ronaldo's new team being placed in the same group as his former club Manchester United.
He stands to miss Juventus' next game at home to Young Boys on October 2 but if UEFA decides to increase the suspension, which is typical for an offence of violent conduct, he will have to sit out one or both of the matches against United.
Jose Mourinho's side host their Italian rivals on the third match day on October 23 before heading to Turin two weeks later.
Elsewhere, Ajax won 3-0 at home against AEK Athens. Nicolas Tagliafico was on target either side of Donny van de Beek's strike for the Dutch side.
Later in Group E, goals from Robert Lewandowski and Renato Sanches saw Bayern Munich win 2-0 at Benfica.