"He is focused. When you have treatment on the medical bench it's not easy".
Sanchez returned late to pre-season training with the Gunners due to his commitments at the Confederations Cup with Chile and will now have his start to the new Premier League campaign delayed.
Manchester City and Paris Saint-Germain are reportedly interested in the player, who has just one year left on his contract at Arsenal.
It would therefore appear that one more season with Arsenal and a free transfer next summer to the club of his choosing is now the most likely outcome for Sanchez.
Having ended months of speculation by signing a new two-year contract, he is looking forwards and says that if the team put on a united front, the fans will fall into line behind them.
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Wenger insists he will not relent on Sanchez's future though, claiming nothing has changed from last season and that he will not be sold.
"I think he had in his career some bad moments because he had some small injuries", the manager added.
The leader of "Arsenal" Alexis Sanchez could become the highest paid player in the English Premier League.
Now Sanchez is a hard choice - to sign the main contract of his life or go to another club who set themselves more ambitious goals.
The Frenchman also dismissed media reports linking Alex Oxlade-Chamberlain with rival Chelsea.
The Premier League's longest-serving manager also touched upon his indecision regarding extending his Arsenal contract last season, suggesting it created an unease amongst his players. "For example Ramsey, Ozil, Mertesacker, and, of course, Koscielny is suspended. I have players coming back who have not played like [Shkodran] Mustafi and Sanchez".