Howard said New South Wales' decision to include rugby league player Andrew Johns in its Twenty20 team to face South Australia in January, showed Twenty 20 was "entertainment, not serious cricket".
"It's not for me to say you can't do it," Howard told commercial radio. "I don't run cricket, I only follow it and love it. It's up to the people who run it.
"It does draw an audience and I'm a cricket traditionalist, but if it brings new people into the game, that's great, but don't expect me to be a spectator at Twenty20, thank you."
NSW cricketing authorities have admitted including Johns, considered the world's best rugby league player, is an attempt to increase crowds.
But the move has angered purists and attracted criticism from Cricket Australia, which said it does not need such gimmicks to promote the game.
Howard said he would never consider participating in a Twenty20 game.
"Id only be available for an Australian team but I dont think Id get chosen mate," he said.
The International Cricket Council will stage the inaugural Twenty20 World Championship in South Africa in September 2007.