After the conclusion of the Champions League group stage on Wednesday night, a number of quality teams dropped into the second tier of the competition after finishing third in their group, including Celtic, Napoli and Atletico Madrid.
The Gunners take on BATE Borisov on Thursday night at the Emirates.
But with qualification already secured, Keown believes a meeting with the Bhoys would test the quality of their Scottish opponents.
"I think just for the credibility of their own Scottish division, they need Celtic to do well.
"They didn't do well in the Champions League. It starts to hot up, Atletico Madrid of course will fancy their chances.
"Arsenal, of the teams currently in the Europa League, have probably been the best team."