Barca have not won the Champions League since Xavi left in 2015 and Messi is out of contract at the end of next season, although the Blaugrana are confident he will sign a new long-term deal.
"He has earned it," Xavi told El Pais. "[There should be an] automatic clause. Messi needs Barca and Barca need Messi.
"They have to make him happy, because with Leo Messi content, they will win more trophies.
"I maintain a great friendship with him, I respect him a lot. He's a competitive animal, he always wants to win, and for 10 years he has been the best footballer in the world."
Xavi turned down the chance to replace Ernesto Valverde at Barca in January, but the 40-year-old has made no secret of his desire to coach the club in future.
"Let's hope our paths cross again on a professional level," he said in reference to Messi. "Having the best player in the world in your team is like having an ace [in your hand]."