Alexis was caught on camera laughing after he was substituted, as the Gunners crashed out 10-2 on aggregate.
But Cech says the accusations are “disrespectful”.
“It is sad and he was as sad as I have seen him,” Cech said.
“Unfortunately when you say the sentence, ‘Had we scored the second goal everything could look different’ and then you do ‘ooph’ [exhale] you know, but in the end the reality is you are 5-1 down and somebody twists it and says you are laughing on the bench.
“I found it very disrespectful to the player. But obviously you can take the picture and you can interpret it the way you want unfortunately. But we the players, we know exactly what he said and we know how he was hurting and he was as disappointed as anybody else. It is unfortunate and disappointing.”