Neymar, 22, moved to the Catalan outfit from Santos in the summer, but has struggled to reach the heights of his early-season form since the turn of the year.
"Every player has good and bad periods," Romario said on his official Twitter account.
"The advice I would give him is to show a good attitude and leave his problems off the pitch. He is playing alongside one of the best players in the world and he can learn from him.
"I was the Messi of my day and players used to like learning from me!"
Romario played for Barcelona between 1993 and 1995.