Well, as luck would have it, the Gunners were pitted up against Atletico Madrid in the semi-final draw which was held on Friday afternoon.
It is expected Costa will at least miss Sunday's LaLiga clash with Levante, while he is also likely to be a doubt for the following two games against Real Sociedad and Real Betis.
Arsenal and Marseille will both be at home in the first legs which take place on April 26 with the return games on May 3.
Marseille will host underdog Salzburg in the first leg of the other semifinal. A potential home match with a trophy on the line.
Former Barcelona and France defender Eric Abidal, the Europa League final ambassador, conducted the draw. "Maybe it's better I don't wish for anybody and just wait for the draw tomorrow". The London side won 6-3 on aggregate.
Ligue Europa : Marseille-Salzbourg et Arsenal-Atlético en demi-finales
Les deux favoris, Arsenal et l'Atlético Madrid, vont se mesurer dans le choc des demi-finales de l'Europa League de football. Pour ce dernier carré, le match à suivre sera certainement l'opposition entre Arsenal et l'Atletico Madrid.
Arsenal currently sits in sixth place in the Premier League, while Marseille is fourth.
Diego Simeone wants to sign a new forward and Paulinho is one of the names at the top of his wishlist.
However, they were knocked out of the respected group in the Champions League and have taken the competition by storm.
Los Rojiblancos have impressed in their short stint in this year's Europa League after dropping out of their Champions League group. The final will be played on May 16 in Lyon.
Yet in the quarter-finals, they seemed to become complacent after allowing Sporting back into the tie having not shown their usual clinical finishing.
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