It has been a mixed campaign for the Argentine forward due to a two-month spell on the sidelines.
Messi has still scored 38 times for the Catalan outfit this season, but has been criticised in recent weeks for a perceived laziness in matches.
"Messi has to overcome the sadness of poor performances and rediscover the joy, pride and passion it takes to play at a club like Barcelona," AS quotes Menotti as saying.
"I've seen more mental fatigue than physical. It's normal when there are a lot of games and he has many obligations.
"Maybe a couple of days rest would help him recompose his head and be the best in the world again."
Messi will be in action this evening as Barcelona face Real Madrid in the final of the Copa del Rey.