Costa left Chelsea at the end of the 2016-17 season following a row with Conte and returned to Atletico Madrid -- the club he had left to join Chelsea in 2014.
Conte followed Costa out of Stamford Bridge 12 months later and took a year out of football, during which time he was heavily linked with the Real Madrid job, before he was named Inter Milan boss in May.
"We [Conte and I] had problems off the pitch, but I think he is a really good manager," Costa said. "I have no hard feelings towards Conte.
"But to be a top, top manager, he needs to change the human side of his management. He is very suspicious. At a like, say, Real Madrid, he would never last a season."
In 2013, Costa declared he would represent Spain at international level despite having been born in Brazil and making two appearances for the South Americans.
The 31-year-old was widely criticised in the country of his birth for his decision to play for Spain, but said he opted for switch due to being overlooked by then Brazil manager Luiz Felipe Scolari.
"After the friendly against Russia, he said he would call me up again because I hadn't played many minutes," he added. "I think it was just to get in my head.
"I remember several forwards were injured but Scolari would not select me. I stayed quiet, but wasn't selected for the Confederations Cup. The possibility of Spain emerged and I accepted.
"How could I say no? Suddenly, they started saying Scolari wanted me. Well, he never called me once. How could it be that he wanted me? I then saw it written that I had ruined the dreams of millions of Brazilians.
"Why not say that he didn't look for me? Then it's simple."