The Pimco Total Return Fund posted $4.3 billion in net outflows in May, its 13th straight month of investor withdrawals, according to Morningstar data. The fund has seen $59.6 billion in outflows since May of last year.
"Pimco had a rough patch, I guess, towards end of 2013, now it's not a rough patch," Gross said in an interview with CNBC's " Street Signs ."
"We're moving ahead. I couldn't be more confident by the end of this year that Pimco will be close to the top of the pack in terms of the bond market. And those that are taking money out, well, hopefully they will be putting it back in real soon."
Gross pointed out that the fund is outperforming.
"Look in May and look in early June. And watch our 12-month numbers ... over the next week or two, they're going to be in the 75 percentile."
-By CNBC's Michelle Fox