The ex-Barca winger has encouraged the reigning Spanish champions to make a move for the Brazil international this summer
The 66-year-old feels Barca rely too much on Messi at the moment and has stressed that it would benefit the team if they had another player who can make the difference such as Neymar.
"Neymar is a different kind of player. We can't be too reliant on a single player, which is the case with Messi," Rexach told Marca.
"The solution is to look for another decisive player, because it looks like Barca gets into trouble when Messi's injured.
"Signing him might get more expensive, because [Real Madrid president] Florentino Perez wants him as well."
The 21-year-old has a contract with Santos until after the 2014 World Cup, but will travel to Barcelona after the Confederations Cup to discuss a potential transfer this summer.
Ex-Santos official Vicente Cascione claimed on Tuesday that the Brazil international has already signed for Bayern Munich but the Bundesliga immediately issued an official denial.