Chilean superstar Sanchez appeared to be smirking on the bench as the Gunners fell to a second 5-1 loss to the German giants earlier this month.
But Cech insists Sanchez was just as devastated as the rest of the Arsenal team after the Emirates mauling.
The goalkeeper said: ‘It is sad and he [Sanchez] was as sad as I have seen him.
‘And unfortunately when you say the sentence, “had we scored the second goal everything could look different” and then you know.
‘But obviously you can take the picture and you can interpret it the way you want unfortunately.
‘But we the players 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.’
Sanchez has been strongly linked with a summer move after cutting a frustrated figure at the Emirates in recent months.
The playmaker was dropped for Arsenal’s trip to Liverpool earlier in the month after reportedly being involved in a series of training ground rows.
Premier League rivals Chelsea and Manchester City are believed to be considering summer swoops for Sanchez, but the Gunners will look to prevent their top goalscorer from joining another English side if they are forced to sell him at the end of the season.