The five-time Ballon d'Or winner has spent his entire career at the Catalan club, winning 29 trophies since making his first-team debut at the age of 16 in 2004.
Guardiola coached the Argentine for four years during his spell as Barcelona boss, and the 45-year-old appears to have opened the door to a possible transfer for the prolific player.
"I never called Messi and I wish him to play here and finish his career here, but maybe he wants to go somewhere else. Maybe he wants his kids to speak English," Guardiola told reporters in Tuesday's press conference.
"If it happens, there would be a list of six, seven or eight clubs who would want to sign him, but it will be down to Messi where he wants to go."
Guardiola also stressed to the media that he did not try to lure Barca's best players to the Etihad Stadium during the summer transfer window.
The Spanish coach will face his former club on Wednesday night in a Champions League encounter at Camp Nou.