Aguero has joined Barca from Manchester City this summer, while Messi's new contract is expected to be signed within the next week.
Via Sport, Menotti declared on Super Deportivo Radio: "Agüero and Messi will become even closer friends at Barcelona. I am looking forward to seeing them together. I laugh a lot when I see them together."
Indeed, Menotti believes the presence of Aguero will lift the spirits of Messi after he saw good friend Luis Suarez forced out of the club last summer. The Uruguay striker eventually signed for Atletico Madrid, helping them to the LaLiga title last season.
For his part, Menotti remains baffled by the decision from Barca to let Suarez go.
He continued: “It's what life is like, right? Messi was a great friend of (Luis) Suárez, I still don't know what Barcelona did to let him go, something that I think Messi felt a lot. And now Agüero appears, with whom they are always together, with whom he has a very healthy relationship.
"Messi is going to be happy with this crazy man who is divine, because he is funny and also does not have anything strange. He is a character, a charming boy, very healthy."
Aguero and Messi were together this summer as they drove Argentina to victory in the Copa America in Brazil.
- updated July 28