They'll play Granada and Slavia Prague respectively.
Arsenal boss Mikel Arteta hopes his players respond to the criticism they received following their 3-nil defeat to Liverpool, when they host Slavia Prague in the Europa League quarter-finals later.
Pundit Jamie Carragher called on him to "get rid of Alexandre Lacazette, Willian and Nicolas Pepe", while Gary Neville described them as "flaky".
Arteta wants the team to prove them wrong in this evening's first leg:
Manchester United boss Ole Gunnar Solskjaer admits Europa League success is now critical to their season.
They're in Spain tonight to face Granada in the first-leg of their quarter-final clash.
Having previously played down the importance of silverware, Solskjaer says his players know it's a vital competition.