Bulgaria coach Krasimir Balakov has resigned days after home fans at Vasil Levski Stadium directed racist abuse at England players during a 6-0 defeat to Gareth Southgate's side.
The Bulgarian Football Union (BFU) announced the news in a statement on Friday.
Also Friday, five more Bulgarian fans were detained and the interior ministry said police had so far identified 16 people believed to have taken part in the abuse.
"Five more men implicated in the abusive actions were detained this morning," the ministry said. "Police continues work to track down five more to detain them."
Balakov's resignation follows that of BFU president Borislav Mihaylov, who stepped down this week after Bulgarian Prime Minister Boyko Borissov urged the former goalkeeper to do so.
Balakov said after Monday's game in Sofia that he had not heard any racist abuse aimed at England's black players, but the Euro 2020 qualifying fixture was temporarily halted during the first half in order to warn supporters that the match could be abandoned following racist chanting.
Match referee Ivan Bebek instructed the stadium public-address announcer to broadcast the message -- the first step in FIFA's three-step protocol when dealing with such incidents -- after England defender Tyrone Mings said he was the subject of racist chanting in the 22nd minute.
The match then continued, but play was stopped again on 41 minutes, when Southgate was involved in another lengthy discussion with the referee.
Bulgaria supporters in the crowd were seen directing monkey chants at England players, making Nazi salutes and holding up shirts with the UEFA logo and the text "No Respect" -- a reference to the European governing body's "Respect" campaign aimed at curbing racism in the sport.
Balakov said on Monday: "I was concentrated on the game.
"I didn't actually hear anything, but I just talked to the English press downstairs and I told them that if this is proven to be true, then we have to be ashamed and we have to apologise for it.
"But, once again, first it has to be proven to be true."
He later issued a statement making a "sincere apology" to the England team and anyone else offended by the racist abuse.
The Associated Press contributed to this report.