Sanchez now has just one year remaining on his contract with doubts over his future at the club casting a shadow over Arsenal's 2016-17 campaign last term. The Gunners' failure to qualify for next season's Champions League saw those concerns grow, with Manchester City reportedly confident of completing a deal for the Chile international.
Arsene Wenger has remained resolute over his forward's future, however, insisting Sanchez, who scored 30 goals in all competitions last season, has not asked to leave the Emirates Stadium this summer.
Likewise, Mertesacker feels there should be no doubts over his teammate's future at the club. When asked by Fox Sports whether Sanchez will stay at the club, he responded emphatically: "Yes, definitely.
"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 are talking about championships, to keep our best player is key. I think he was impressive in the Confederations Cup, he is now on holiday, so it is quiet in terms of conversations.
"But he is a warrior on the pitch. I think he wants to come back as quickly as possible – he hates holidays, he hates to calm down. I am looking forward to playing alongside him in my last season and he thinks the same."
Recent reports suggest Sanchez is seeking an offer of £400,000 per week to sign a new deal in north London. While City have been tipped as favourites to sign him if he is to leave, Chelsea have also been credited with interest with Sanchez himself reportedly open to the idea of moving across London.
Speaking at a press conference on Tuesday morning, however, Wenger insisted the player has not asked to leave, adding: "The easiest way to manage the players in the final year of their contracts is it's in his interest to do as well as he can," he explained.
"Nobody knows today if Sanchez will be in the final year of his contract next season because he can as well extend his contract with us at the start of the season or during the season.
"It's not necessarily the last year of his contract at Arsenal football club."