Zenit St Petersburg and Fiorentina are among the sides aiming to book their place in the UEFA Europa League semi-finals.
Kevin de Bruyne rescued a point for Wolfsburg against Schalke as they lost ground on leaders Bayern Munich.
Wolfsburg lost ground on Bayern Munich at the top of the Bundesliga after being held to a 1-1 draw by Schalke.
Marek Hamsik scored twice as Napoli took a giant step towards the Europa League semi-finals by beating Wolfsburg 4-1 away.
Wolfsburg returned to within 10 points of Bundesliga leaders Bayern Munich with a 2-0 win in Hamburg.
Wolfsburg all but mathematically secured a Champions League spot with their 3-1 win over Stuttgart.
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