Barca have raised eyebrows around Europe over the past few transfer windows with several signings that weren't particularly in line with the club's philosophy in the form of Paulinho, Arturo Vidal and more recently Kevin Prince-Boateng.
However, with the arrivals sparking more competition in the squad with veteran performers, the signings of Jean-Clair Todibo, Clément Lenglet, Arthur Melo and the £65m (R1.15bn) agreement to sign Frenkie de Jong points to the long-term view of sustaining success at the Camp Nou.
Messi, 31, graduated from the club's academy and has gone on to score 581 goals in 664 games for the Blaugrana and is widely considered as one of the greatest footballers of all time.
"I know one day Lionel will say he's retiring," Bartomeu told the 5 live Football Daily Podcast.
While Messi still has another two years left on his current contract Bartomeu has conceded he's given no indication of when he'll hang up his boots - but confirmed 'it's a while off from now'.
However, the 25-time La Liga champions are not resting on their laurels as they target some of Europe's most highly-rated prospects to ease the five-time Ballon d'Or winner out the team before his eventual retirement.
"We have to prepare the club for the future," added Bartomeu, who is due to step down as president in 2021.
"We are bringing great young players to the team because we need to continue this era of success. That's our responsibility.
"My mandate will be finished in two seasons. So I need to leave the club in a great position and tell the new president 'that's our legacy'."
Messi has won nine La Liga titles with Barcelona as well as four Champions League titles and six Copas del Rey.