El-Erian stunned markets when he abruptly resigned as CEO of asset manager Pimco in January. Soon, reports emerged of tensions between him and Gross, the chief investment officer long revered for his prowess in the bond markets.
Those tensions came to a head Thursday when Gross told Reuters he had been monitoring El-Erian's phone calls and that El-Erian was trying to "undermine" him.
The tension over Gross's relationship with El-Erian has been exacerbated by his performance of late. In recent months Gross's flagship Total Return Fund has lagged most of its peers.
After losing nearly 2 percent in 2013—one of the strongest market years in history—some question whether Gross has lost his touch.
El-Erian has thus far been largely silent on Gross's claims. Many have speculated about his next move—US government service, or perhaps some sort of public position in his native Egypt.
Pimco's usually active Twitter account has been silent on the spat so far Friday morning. (Pimco emailed Reuters a statement in which it said: "Mr. Gross did not make the statements Reuters attributes to him.")
That hasn't stopped others, though, from commenting on the unusual spat.
The chart in this story has been updated to reflect the Pimco Total Return fund's correct performance in January.