NEW YORK -- The Pimco Total Return Fund, the world's largest bond fund run by Bill Gross, is ending the month on a rough note, lagging 93 percent of its peers so far in July.

According to preliminary Morningstar data on Thursday, the Pimco Total Return is posting returns of negative 0.49 percent, while its peer-fund category is putting up returns of 0.26 percent on the month as of July 30.

Gross's fund performance is widely followed as it serves as an industry benchmark, though this year has been one of Gross's roughest patches. Gross saw his successor, Mohamed El-Erian, resign earlier this year while his Pimco Total Return has seen over $64 billion of net outflows since May 2013.

"The Pimco Total Return Fund (PTTRX) has a lot of duration exposure to the 1-5 year point of the yield curve, the exact spot where yields rose during July," said David Schawel, vice president and portfolio manager of Square 1 Financial.

"Meanwhile, they show to have just 11 percent of maturities over 10 years, areas which rallied the past month."

Gross has maintained all year his position on favoring shorter-maturing debt. He has repeatedly said fixed-income securities maturing in five years to 30 years were "at risk" given reduced bond buying from the Federal Reserve.

Gross said these bonds that the Fed "has been buying will have to be sold at higher yields to entice the private sector back in."

But the long end of the Treasury yield curve has been performing well.

In July, the Barclays Capital U.S. 20 Year Plus Treasury Bond Index posted returns of 2.25 percent. For the year, the Barclays 20 Year Plus is up 15.73 percent.

The Pimco Total Return Fund had $225 billion in assets at the end of last month, down from a peak of $292.9 billion in April 2013.