Arsenal will face Napoli in the quarter-finals of the Europa League.
The Gunners, who are third favourites for the competition behind Chelsea and the Italians, will host Napoli for the first leg on April 11, before the return leg in Naples a week later.
They were drawn to play away first but because Uefa do not allow teams from the same city to play at home on the same day, Arsenal's tie has been switched so their second leg is not played in London on the same night as Chelsea's.
If Arsenal get through to the semi-finals they will play the winners of the all-Spanish quarter-final, Valencia v Villareal.
London rivals Chelsea look to have a much simpler task, being drawn against Slavia Prague.
Speaking after the 3-0 win over Rennes on Thursday night put the Gunners into the quarter-finals, boos Unai Emery said: "The Europa League is giving us a big opportunity to take one way towards the Champions League.
"There is one title. I said to the players today, it is exciting in the competition, but it is not only exciting to get to the Champions League in this competition, it is also because it is one title."
The draw in full is as follows: Napoli v Arsenal, Villareal v Valencia, Benfica v Eintracht Frankfurt, Slavia Prague v Chelsea.