Super Rugby expanded to 18 teams this year, with a sixth South African side, the Kings rejoining the competition, while it also moved into new markets in Japan and Argentina with the Sunwolves and Jaguares.
All three sides have struggled this season, which stirred debate about whether the competition had overstretched, while rugby pundits in New Zealand have also questioned the depth of teams in Australia and South Africa.
"We've set this conference structure up so that future expansion will be possible and more sensible in terms of travel and workload, but we've got to break into new markets," Tew told Radio Sport from London.
"When we go to the next set of broadcasting deals we've got to be sure we've got a footprint in South America, that we've got a footprint in Asia, and possibly other markets or we will go bust, because we continue to compete against the clubs up here."
Tew said it was important to broaden Super Rugby's horizons as people could turn their attention to other sports and players would head for Europe.
"If we want to play professional rugby, we can't just play ourselves - we will go out of business very quickly," he said.
"We can't just play Australia, because the same will apply, it will just take a little bit longer to get there.
"So we have to have a competition that involves other countries, and by geography, that's complex."
Andy Marinos, the head of the competition's governing body SANZAAR, told reporters on a recent conference call there was unlikely to be any expansion until the conclusion of the current broadcasting agreement that expires in 2020.
It would, however, keep a close eye on the growth of the North American professional competition, which was launched last month with five teams in Ohio, Colorado, and three in California.
"North America is certainly a very interesting market to look at but at this stage we have no view on how expansion might look," Marinos said.
"Where we're currently sitting, (18) is the number of teams we've sold into our broadcast and in our promotional model, so that's where we're sitting for the conceivable future."
(Reporting by Greg Stutchbury; Editing by Peter Rutherford)
