Bayern Munich won 5-1 on the night to make it 10-2 on aggregate – the worst two-legged result of any English side in Champions League history.
Up until the 53rd minute, Arsenal were holding a promising position with a 1-0 lead but they completed folded when Koscielny was given his marching orders.
Arsene Wenger claimed Arsenal faced an impossible task when Laurent Koscielny was sent off
Arsenal's 10-2 aggregate defeat was the worst of any English side in Champions League history
And Wenger claims it would have been a totally different result had both teams finished with 11 men.
"It is easy to assess the game," said Wenger.
"We watched it and analysed it.
Twitter reacts after Arsenal suffer humiliating 10-2 (agg) defeat to Bayern Munich
Tue, March 7, 2017
Express Sport brings you all the best tweets as fans react to Arsenal's humiliating 10-2 (agg) defeat to Bayern Munich in the Champions League
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"As long as it was 11 vs 11, we produced a top level performance.
"After that, it became impossible when Koscielny was sent off."