Due to their third-place league performance, Arsenal was paired with either the 13th and 14th slot winners of the play-off ties or the 19th and 20th slot winners.
Following a 1-1 draw at the San Siro on Tuesday, Feyenoord advanced over AC Milan 2-1 on aggregate as Julian Carranza stunned the Serie A powerhouses with an equaliser in the 73rd minute.
To guarantee the eight unseeded teams in the round of 16, the teams ranked ninth through twenty-four were forced into a play-off stage - which saw the games completed over the past two weeks.
The top eight clubs advanced directly to the round of 16 under the new league phase format, avoiding a two-leg play-off match.
On Wednesday, Juventus led PSV 2-1 going into their second leg in Holland, but the Dutch champions rallied for a 4-3 aggregate victory after extra time.
