Four-time Olympic champion Mo Farah and Haile Gebrselassie are involved in a dispute over an alleged theft at a hotel belonging to the Ethiopian athletics great in Addis Ababa.
The Briton said he had money, a watch and two phones taken from his room, and that Gebrselassie did not help him.
"I was just disappointed with Haile," said 36-year-old Farah.
Gebrselassie, 46, responded by accusing Farah of "blackmail" and "defaming" his reputation and business.
Farah made the claims at the media preview event of Sunday's London Marathon.
"Just to be honest, it's Haile who owns the hotel and when you stay for three months in that hotel, it was very disappointing to know that someone who has that hotel and that kind of support couldn't do nothing," said Farah, who had been training in Ethiopia.
Farah alleged that the items were stolen on March 23.
In a statement sent to BBC Sport via his agent, double Olympic 10,000m champion Gebrselassie said he was considering taking legal action against Farah.
He said a text message he received from Farah before the London Marathon news conference was an attempt to "blackmail" him.
Gebrselassie said guests staying at his hotel are asked to declare if they are carrying more than $350 (£271) in cash, so they could be given the option of keeping the money in a safe box or give it to officials for safe-keeping.
He claimed that Farah chose to hold on to his money, which meant his hotel was not legally accountable for it.
Gebrselassie said the alleged theft was reported and that five of the hotel's employees were investigated but released without charge, adding that police "found nothing on the reported robbery case".
Gebrselassie, who won four world titles, said Farah was given a 50% discount on his hotel rates, but left without paying his service bill of 81,000 Ethiopian Birr ($2,806).
He also said his hotel staff reported "disgraceful conduct" by Farah and his entourage and that he was reported to the police for "attacking a married athlete in the gym".
Gebrselassie said a criminal charge was dropped because of his own mediation role.
'Farah wants matter resolved'
In response to Gebrselassie's claims, a spokesperson for Farah said: "Mo is disappointed with this statement and the continued reluctance by the hotel and its owner to take responsibility for this robbery.
"Mo disputes all of these claims, which are an effort to distract from the situation, where members of his hotel staff used a room key and stole money and items from Mo Farah's room (there was no safe as it was faulty, and Mo requested a new one).
"Police reports confirm the incident and the hotel admitted responsibility and were in contact with Mo's legal advisor.
"The hotel even offered to pay Mo the amount stolen, only to withdraw the offer when he prematurely left the hotel and moved to other accommodation due to security concerns.
"Despite many attempts to discuss this issue privately with Mr Gebrselassie, he did not respond but now that he has, we would welcome him or his legal team getting in touch so that this matter can be resolved."