The 50-over World Cup is scheduled to be held in India later this year.
Shastri called for a change in the year of the ODI World Cup, scheduled to be held in India in October-November.
"For One-day cricket to survive, I think it should be reduced to 40-over game in future," said Shastri on Day 4 of the fourth India-Australia Test in Ahmedabad.
"The reason I say this is because when we won the World Cup in 1983, it was a 60-over (a side) game. Then the attention span of the people diminished and it became a 50-over game. I think the time has come for it to become now a 40-over game. Evolve with the times. Reduce the format,” he added.
Ravi Shastri also opined that the bilateral T20I series between countries should be reduced as franchise leagues around the world are enough to promote the shortest format.
"T20 format I think is the key. It is the injection the game needs to evolve. It's the cash cow for the sport. But I think there also the bilaterals (series) should be reduced. There are enough domestic leagues around the world that promote the T20 game.
"We should let those leagues happen and then have a World Cup, just in between. Very few bilaterals, if needed before a World Cup or something of that sort. Then you can sustain all three formats," he stated.
Every now and then, cricket pundits express fear over the future of Test cricket. However, Shastri reckons the longest format will continue to flourish.
"Test cricket will remain Test cricket and it should be given paramount importance. It's the real thing. I think there's a place for all formats within India. Especially in the subcontinent. Especially in places like Australia."
Veteran India wicketkeeper Dinesh Karthik also echoed with Shastri’s views on ODIs, saying that the 50-over format is losing its charm and the World Cup in India later this year could be the last edition.
"ODI format has lost its charm. We may see the last World Cup later this year or maybe one more after that. People wants to see Test cricket, which is the truest form of cricket and T20 for entertainment," said Karthik.
"Test cricket is like art movies and T20 is commercial cinema. ODIs are present in no man's land. Take the example of Ben Stokes, the best all-rounder of the current times saying he is done with the ODI cricket.
"There is a fact that with a T20 World Cup scheduled every two years, countries will not be playing bilateral series anymore. There won't be enough ODI matches," he added.
(With PTI Inputs)