Bill Gross, manager of the world's largest bond fund at Pimco, said today that income, rather than capital gains, would drive future investment returns as a result of low global economic growth.

"Capital gains from almost all asset classes are approaching dusk. Low but relatively dependable income will be the market's future driver," Gross, the chief investment officer of Pimco, said in his latest monthly letter to investors titled "Goodnight Vietnam."

Income is the interest payout on an asset, whereas capital gains are price gains on an asset. Gross said a lack of aggregate demand and a "continuing surfeit of supply" would continue to weigh on global growth rates.

Gross's views are closely watched because his flagship Pimco Total Return Fund is the world's biggest bond fund, with $225 billion in assets. Pacific Investment Management Co. altogether had $1.97 trillion in assets as of June 30, according to the firm's website.

Gross's comments were in line with Pimco's 'New Neutral' outlook for the global economy, which the firm introduced in May. New Neutral suggests the global economy is transforming from a post-financial-crisis recovery period called the New Normal in 2009 toward stability characterized by modest economic growth over the next three to five years.

Gross's Total Return Fund is up 3.62 percent so far this year, trailing 77 percent of its peers, according to data from Morningstar.