Pienaar, who is in his first full year as player-coach at Saracens, is worried the rugby investment boom will soon drain away if financiers do not quickly see returns on their outlay.
"The game cannot sustain itself in its present form and before long we will see clubs going under," he said during a visit to the London Motor Show.
"Players' salaries are going up and up, so we must be able to play attractive rugby and plenty of it.
"It's crazy that we have had a six-week lay-off just to play in the European Conference. We should have been playing club rugby to get the supporters in.
"The game must find some structure, because we are paying massive bills and the revenue is just not there. We have television and corporate sponsorship, but we still don't have the fans in the stands.
"Rugby does not have the support base that it does in the southern hemisphere and that must be improved."
Pienaar wants a clear-the-air meeting between the new Cliff Brittle regime at the Rugby Football Union and the Premiership clubs to sort out the problem well before next season.