His comments come as global central bankers step up their actions to stimulate growth, particularly inflation. For instance, the BOJ recently announced an unconventional plan for "yield curve control," which aims to keep its benchmark 10-year note yield at zero.

Estimates put the total of negative-yielding debt upwards of $11 trillion, though Gross figures it's closer to $15 trillion, posing a looming specter to markets.

"Ultimately though, in broader, more subjective terms, it is capitalism itself that is threatened by the ongoing Martingale strategies of central banks," Gross said, referencing the bettor strategy of doubling down bets in blackjack with the idea that ultimately a winning hand will come along.

"As central bank purchases grow, and negative/zero interest rate policies persist, they will increasingly inhibit capitalism from carrying out its primary function — the effective allocation of resources based upon return relative to risk," he said.

Gross' $1.5 billion Janus Global Unconstrained Fund has gained just shy of 5 percent this year, putting it in the top third of its peers but slightly behind the 5.8 percent S&P 500 return, according to Morningstar.

His most recent comments are a carryover of recent admonitions for investors to ditch most stocks and bonds and instead focus on gold and real assets.

"Central bankers have fostered a casino like atmosphere where savers/investors are presented with a Hobson's Choice, or perhaps a more damaging Sophie's Choice of participating (or not) in markets previously beyond prior imagination," Gross wrote. "Investors/savers are now scrappin' like mongrel dogs for tidbits of return at the zero bound. This cannot end well."