Messi has agreed to sign a new contract with Barcelona, though the five-time Ballon d'Or winner is yet to officially put pen to paper.
With Messi's signature missing from the Barca contract, the Argentine star has been linked with Guardiola's City in the Premier League.
Asked whether Messi's buyout clause could be activated following Neymar's €222 move to Paris Saint-Germain, Guardiola responded: "I don't know. Someone might have if they have the money and want to spend it.
"It might happen."
Guardiola was speaking after 10-man City's 1-1 draw at home to Everton on Monday.
Raheem Sterling struck late as City salvaged a point against Everton, who also finished with 10 men following Morgan Schneiderlin's late dismissal, after Kyle Walker was sent off in the first half.
Wayne Rooney's 200th Premier League goal had put City on the backfoot until substitute Sterling volleyed past Jordan Pickford to equalise with eight minutes remaining.
"We are here for the results, at least to win games. And to take a result," said Guardiola, who refused to discuss the performance of referee Bobby Madley.
"Sixty minutes with 10 against 11 quality Everton players. I prefer to win the game. We want to start good at home. We had chances again. They had one on the target. They scored a goal.
"We create chances, before the goal, three or four. Brilliant players closing, [Phil] Jagielka, [Michael] Keane — 10 against 11 for 60 minutes against Everton is always difficult, we never give up."