The 1978 World Cup-winning coach is adamant the forward is not intentionally taking things easier in matches in order to rest prior to this summer's tournament in Brazil
The prolific attacker has received his fair share of criticism following poor performances against Atletico Madrid and Granada, with former Barca boss Radomir Antic suggesting the player deliberately took things easier against Atleti due to frustration at being played on the wing.
Menotti, however, has laughed off suggestions that his compatriot is intentionally working less hard to save himself for the summer, instead claiming the 26-year-old is suffering from a mental exhaustion at present.
"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," Menotti told La Xarxa.
"I don't believe that he is saving himself for the World Cup. I get the feeling that he is not clear in his head. I don't think his form has anything to do with the World Cup.
"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 has netted 38 goals in 40 appearances in all competitions for Barcelona this season.