The Athletic was the first to report the news. The sources requested anonymity because they were not authorized to publicly discuss the matter. A league spokesperson declined to comment.
The allegation stems from an incident that occurred on July 15 during the second half of a match between DCU and the New England Revolution.
Around the 67th minute, Fountas, who is white, and Robertha, who is Black, can be seen arguing. The disagreement carried into the locker room after the match, with Robertha allegedly striking Fountas with a foam roller, a device commonly used for treating muscle injuries, the Athletic reported.
Later, Robertha is reported to have told team officials that Fountas used the N-word, which the club immediately communicated to league officials, resulting in an investigation.
Fountas and Robertha were initially placed on administrative leave, although Robertha was reinstated on July 24. The results of the investigation haven't yet been made public. Fountas remains on paid administrative leave.
This is the second time in 10 months that accusations of racist behavior have been leveled at Fountas.
In a league match against Inter Miami last Sept. 18, Fountas was alleged to have directed a racial slur at then-Miami defender Damion Lowe, which was overheard by Miami's Aimé Mabika. A subsequent investigation conducted by MLS found Mabika's allegation "credible" but because it couldn't be corroborated, no fine was issued to Fountas.
The Athletic reported that in a bid to clear his name following the latest allegation, Fountas underwent and passed a polygraph test, the results of which he passed on to the league. The accuracy of polygraphs has long been debated, and are not considered to be conclusive proof that the subject is either lying or telling the truth.
According to data from the MLS Players Association, Fountas, a Greece international, is D.C. United's third-highest-paid player, with a guaranteed compensation of $1.741m.
If Fountas' contract is terminated, the corresponding salary budget space and Designated Player spot would be freed up. But in terms of finding a replacement, DCU would be limited to players out of contract since the summer transfer window closed on Aug. 2. League rosters are set to be frozen on Sept. 13.