Joe Jackson says he doesn't believe his pop singer son, Michael, was ready to start his upcoming 50-date London concert series when he died.

Michael Jackson, 50, was scheduled to begin his residency at the O2 Arena Monday, but died June 25 of cardiac arrest following a suspected drug overdose.

While concert promoters said the popular recording artist was in great form during rehearsals, his father contends he wasn't healthy enough to headline so many shows and was pushed into doing more than he intended.

"The comeback tour was a good idea, but the wrong idea about it. There was more tours added onto it," Joe Jackson told ABC News. "Michael told me himself that he agreed to 10 shows. But they went and added all these other shows. ... I was worried about his health because all the shows that I'm seeing -- no artist can do those many shows you know, back to back like that ... . And so I knew Michael couldn't do all those shows."

Both Joe Jackson and his daughter La Toya have said they think Michael's death was the result of foul play, although officials maintain they are waiting for toxicology tests to come back before they categorize the manner of his death.

"I just couldn't believe what was happening to Michael," the show business family patriarch told ABC News. "I do believe it was foul play. I do believe that. Yes."