The Janus Global Unconstrained Bond Fund, overseen by widely followed investor Bill Gross, attracted just $58.6 million in net new cash in April and posted below-average returns, according to Morningstar data on Monday.
The fund, which had assets of $1.5 billion at the end of April, was down 0.39 percent year-to-date as of Friday, underperforming its peer category by 1.83 percentage points for that period, Morningstar said.
"Bill Gross obviously has a brand that resonates with investors but to gather major assets, investors want more - more of a longer track record with more success," said Todd Rosenbluth, director of ETF & mutual fund research at S&P Capital IQ Global Markets Intelligence. "Bill Gross makes vocal investment calls, but investors want to see it translate into long-term results."
Last month, Gross said he placed a wager against German bonds, tweeting on April 21 that German 10-year Bunds were "the short of a lifetime" and that the bet was better than the pound in 1993.
Gross was referring to investors George Soros and Stanley Druckenmiller, who made their names betting against the pound in 1992.
German 10-year Bund yields had set record lows following the European Central Bank's purchases of public-sector bonds on March 9 as part of its trillion-euro stimulus program, with the latest low of 0.049 percent touched on April 17.
Gross has said his Janus Global Unconstrained Bond Fund was "in the trade" as of the last reporting period at the end of March. He also said the risk was "minimal" against the reward and suggested the trade could earn more through leverage.
Gross's investment call proved prescient, with prices on German bonds falling and their yields rising. The yield on the 10-year Bund was at 0.609 percent on Monday afternoon.
Rosenbluth said the latest available details of holdings in Gross's fund, as of March 31, revealed bets on U.S. Treasuries and emerging market debt, which could be "negating any gains made in German Bunds. We just don't know what he has been doing."
Morningstar said his Janus fund was lagging 93 percent of his peer fund category and underperforming the benchmark Barclays U.S. Aggregate Bond Index by 1.21 percentage points.