Rosell brought Neymar to Camp Nou in 2013, but resigned the following year amid controversy over the funding of the transfer and later spent time in prison before being acquitted.
"From a sporting point of view, I would sign Neymar (again)," he told Mundo Deportivo.
And alluding to the Brazilian's controversial move to Paris Saint-Germain in 2017, he added: "But with a contract depending on sporting and social results and behaviour. In writing."
Asked why Messi wanted the forward to return, he said: "Because Messi, who is the best player in the history of football and very smart, wants the best players in the world by his side in order to win everything."
During Neymar's four seasons at Barca, the Catalan club won a total of eight trophies, including the treble under Luis Enrique in 2014-15.