Arsenal cruised to a 3-0 win at OH Leuven but it wasn't enough for the Champions League holders to secure a top-four spot and a direct route to the quarter-finals.
Rene Slegers' side had already secured a play-off place heading into the final matchday but they did still have hope of securing an automatic last-eight spot if they could secure a big win and results elsewhere went their way.
The Gunners played their part as goals from Olivia Smith (18) and Beth Mead (27) put them on course for victory before an own goal from Saar Janssen rounded off a decent evening for the north London side.
Arsenal, who have now secured five successive wins in all competitions, finish the Champions League league phase in fifth and will be seeded for Thursday's draw (12pm) where they will find out whether they will face Atletico Madrid or OH Leuven again in the play-off round in February.
On a comfortable night for Arsenal, Smith fired her side ahead in the 18th minute, escaping two defenders to unleash a shot that was well saved before driving home the rebound for her first Champions League goal.
Leuven were struggling to deal with the pace of Arsenal's attacks and a second went in when Alessia Russo found Mead, who steered a curling shot home.
Smith produced a tame shot from the edge of the area as the chances began to dry up for the Gunners, who were now facing stiffer resistance from the Belgians.
Goalkeeper Lowiese Seynhaeve then kept out a solid attempt by Smith, who was Arsenal's most dangerous player.
When Arsenal's third goal arrived in the 68th minute it came with a dose of luck after Caitlin Foord's cross was turned into her own net by Janssen as the Gunners cruised to all three points in Belgium.
Arsenal star Beth Mead was satisfied with the 3-0 victory at OH Leuven even though it was not enough to secure direct qualification into the Champions League quarter-finals
"We know that Leuven are a really hard team to break down so it was nice to get two goals in the first half," Mead told Disney Plus.
"I thought we played really well and created a lot of different chances. Maybe we could have been a little more clinical, but we're happy to get three goals.
"In a game like this you get a lot of touches on the ball and for me individually I love doing that as a player. Also the team loves being on the ball, so it was a nice game to be a part of.
"I was happy with my own performance. There were some things I was frustrated with, you could probably see that I was. But I'm happy to get the goal, happy to be playing well and happy to get the win.
"We've ended our Champions League campaign up until now really well and finished in fifth, so that's put us in a good position."
The Women's Champions League league phase is over!
Chelsea secured a top-four finish, meaning they go straight to the quarter-finals.
Arsenal and Man Utd finish fifth and sixth respectively. They will be in the play-off round in February and one will face Atletico Madrid, while the other will meet OH Leuven.
They will find out their respective opponents in the draw on Thursday (12pm).
One thing we do know is that if both Arsenal and Man Utd reach the last eight, one of them will face a huge all-WSL showdown with Chelsea. What an occasion that would be!
