Ambani, who was to be part of a group of industrialists accompanying Modi on his first major bilateral visit, outside the sub-continent, sent regrets, government sources said.
While the sources gave no reasons for the move, an RIL spokesperson did not offer any comments.
Adani Group Chairman Gautam Adani, Sunil Bharti Mittal of Bharti Enterprises, Essar Group head Shashi Ruia, Wipro Chairman Azim Premji and ICICI Bank chief executive Chanda Kochhar were among the industrialists who are to travel to Tokyo to participate in the meeting of India-Japan Business Leaders' Forum (IJBLF) on September 1.
The forum is co-chaired by Chairman of Bharat Forge Baba Kalyani.
Maruti Suzuki Chairman R C Bhargava, Kiran Mazumdar-Shaw of Biocon and Oil and Natural Gas Corp (ONGC) Chairman and Managing Director Dinesh K Sarraf are other members of the business delegation.
Sources said while Modi reached Koyto today, members of the delegation will arrive in Tokyo by tomorrow afternoon.