The network wanted Johnson back for the 2010-11 season, which opens Wednesday, but Johnson said the sides could not agree on contract terms.
"It just didn't work out," he said. "I'm really thankful and appreciative to have had the opportunity to work at the Garden. The building opened up so many doors for me in my life and career."
MSG issued a statement that read, "Gus is a very talented broadcaster and has been a part of the MSG Network family for a long time. We wish him all the best and will miss having him on our team."
Johnson, 43, whose high-energy calls have made him a favorite among many viewers, will not lack for work. He covers pro football and college basketball for CBS, boxing and mixed martial arts for Showtime and basketball for the Big Ten Network, and is the voice of the Madden '11 video game.
The busy schedule complicated his availability for Knicks games, but MSG apparently was willing to work around those conflicts to retain him.
Johnson acknowledged the schedule was a challenge. "I never wanted to short MSG in any way or the Knicks in any way," he said. "I am blessed to have so many great opportunities. It got a little hard to deal with them all. I'm only one person. There's a certain part of me that's tired, too."
Mike Crispino likely will handle much of the radio play-by-play. It is not clear how MSG will fill Johnson's role on TV. Kenny Albert frequently filled in for Mike Breen when Breen was unavailable last season.
"They took me out of the sticks and gave me a chance to work in New York when I was very young," said Johnson, who credited Marv Albert, Al Trautwig, Bob Page and Bruce Beck among those who helped teach him the business at the network.
"I will definitely, definitely miss being there. They made every effort that they could [to re-sign me] based on what they had or what their constraints were. Unfortunately, at this time, we weren't able to work it out.
"All I can say is that it was a wonderful experience, an incredible opportunity. Madison Square Garden changed my life."
The Dolan family owns
controlling interests in the Knicks, MSG and Cablevision. Cablevision owns Newsday.