Messi, 33, has made his intention clear that he would like to move on from the club where he's earned legendary status as the captain and the record goal-scorer.
However, the current standoff with the Blaugrana over his release clause could force him to remain until the expiry of his contract at the end of next season.
But Modric, who is familiar with losing a colossal figure, with Cristiano Ronaldo leaving Real for Juventus in 2017, believes their fierce rivals would emerge stronger if their attacking talisman were to depart.
"It would be a huge loss. Like when Cristiano left. But you can't think about the past. It's football and that's it," the 2018 Ballon d'Or winner told AFP.
"If it happens it will be a huge loss for the prestige of the league. But we need to go forward. Other players will become stars.
"When Ronaldo left, the same thing happened, the life of Real Madrid went on without him and it will be the same for Barcelona and La Liga without Messi."
