Chile sit sixth in South American qualifying for the tournament in Russia with two rounds left and only the top four qualifying automatically.
Sanchez wanted to leave Arsenal during the recent transfer window only to see his desired move to Manchester City break down on deadline day and the 28-year-old's frustration at club football is being mirrored on the international stage.
"And tomorrow is coming," Sanchez wrote on his Instagram account.
"You get tired for being criticised with or without reason, you get tired of wanting to be defeated, you get tired of saying to yourself 'once more I'll get up' after crying after a defeat, and you get tired of telling the world and people who are with you, that everything is going well.
"And the worst, is that no one ever realizes how that makes you feel ..
I have the 7 of Chile on my back and it is a huge responsibility, that's why it pains me that journalists and bad people criticize without knowing..."
Sanchez seemed destined for a Â£60million move to City last month but the transfer collapsed and he must see out the final year of his contract at Arsenal, unless he departs in January.
Source : PA