SOFIA (REUTERS) - More than 20 players and officials from two Bulgarian top-flight clubs have been quarantined with novel coronavirus infections following a laboratory mistake, the teams said on Monday (July 6).

Tsarsko Selo defender Martin Kavdanski played in their league game against Cherno More Varna on Thursday despite testing positive for Covid-19.

Kavdanski was named in the starting line-up after the laboratory, which conducted the players' tests, had informed the club and the Bulgarian Football Union (BFU) that all pre-match tests were negative.

However, on Friday the lab admitted it had made a mistake, saying Kavdanski's test was positive, Tsarsko Selo said in a statement.

The club added that three more players - Ivaylo Ivanov, Iliya Dzhamov and Kiril Troharov - had tested positive for Covid-19 after new tests.

Local media reported that Tsarsko Selo's owner Stoyne Manolov has also tested positive for the new coronavirus.

Also on Monday, Cherno More said the Varna-based club had been hit with 16 positive tests for Covid-19.

"Unfortunately, the results found 16 positive samples," Cherno More said in a statement. "All players, who tested positive, are quarantined and we have taken the necessary precautions.

"We have notified the BFU's medical commission as well as the sports and technical department and we are waiting for their instructions."

Despite the 16 positive tests, Cherno More said they are still ready to play their league match at home to Arda Kardzhali on Tuesday, relying on junior players.

As of Monday, the Balkan country had 5,740 confirmed cases of the new coronavirus while 246 people had died.