England batsman Alastair Cook says he understands the proposed 100-ball competition but that Test and first-class cricket should be "protected".
The England and Wales Cricket Board wants to introduce the format into its new city-based tournament from 2020.
"There has to be a place for five-day or four-day cricket," former England captain Cook, 33, told BBC Sport.
"The difference, for me, is the satisfaction of a long game compared to the thrill of a shorter game."
The concept could see innings consist of 15 traditional six-ball overs and a final 10-ball over, with the Telegraph reporting that up to three players could bowl the last over.
Speaking at a Chance to Shine event, Cook said: "There's a bit of caution with me. I still think you have to protect the traditional cricket.
"It's obvious to see how every tournament of that is thriving where Test cricket isn't thriving as it was, say 10 years, ago.
"At the moment, all the money is in the shorter formats of the game. There must be a way of combining the two and protecting Test cricket because of all that it stands for."
Cook has played 154 Tests, scored 12,028 runs, made 32 centuries - all England records - and captained the side in 59 Tests between 2010 and 2016.
'It has a place in the game'
England director of cricket Andrew Strauss has said the 100-ball proposal is aimed at "mums and kids in the summer holidays".
England bowler Stuart Broad praised the concept's "unique selling point", but BBC cricket correspondent Jonathan Agnew questioned what impact it will have on the four-day County Championship.
Test captain Joe Root said players and governing bodies must find a way to ensure other formats "don't suffer" from the new competition.
"It has a place in the game and hopefully over time we will see that," Root told BBC Sport.
"The more people we can get into the sport the better and we've got to be very careful that we don't measure it against the other formats.
"It's something to gather a new audience, gain interest and make it really simple for everyone to understand and not see it as a threat to the other formats."