Sanchez's contract negotiations dragged on during the latter stages of last season but German central defender Mertesacker is confident that the 28-year-old will remain at the Emirates for the next campaign.
"Yes, definitely," Mertesacker told Fox Sports when asked if Sanchez was staying. "We have a strong squad and we do not want to lose any players.
"Even in their final contract year we need them. We cannot afford to lose them. If you're talking about championships, to keep our best player is key.
"I think he was impressive in the Confederations Cup, he's now on holiday... But he's a warrior on the pitch. I think he wants to come back as quickly as possible -- he hates holidays, he hates to calm down."
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Sanchez, who is his country's record goal scorer and helped the team reach the Confederations Cup final earlier this month, had previously expressed his frustration with Arsenal's failure to challenge for the league title.
Arsenal are currently in Australia where they play two pre-season friendlies, starting against Sydney FC on Thursday.
(Reporting by Aditi Prakash in Bengaluru)
