Celtic's Covid-19 frustrations have intensified after Nir Bitton tested positive while away with Israel.
The defender is the third Celtic player to have been instructed to self-isolate while on international duty and the club have vowed to hold talks with national team associations in a bid to minimise the risk of further blows.
Bitton will join Ryan Christie in self-isolating for next weekend's derby clash with Rangers after the Scotland midfielder was identified as a close contact of his international and former Hoops team-mate Stuart Armstrong, who tested positive this week.
Celtic could also be without Odsonne Edouard for next Saturday's Parkhead clash after the striker tested positive while on France Under-21 duty. His self-isolation period will make his involvement in the Scottish Premiership encounter very tight.
Bitton featured against Scotland in the Euro 2020 play-offs on Thursday despite Celtic manager Neil Lennon claiming an ankle injury would have made it impossible for him to play.
Celtic confirmed Bitton had returned a positive test on Friday, ahead of Israel's home Nations League clash with the Czech Republic, who themselves initially travelled with only nine players following another outbreak in their camp.
Clearly, recent events during this international period are very concerning and frustrating
The Scottish champions said in a statement: "Clearly, recent events during this international period are very concerning and frustrating.
"We have worked tirelessly to ensure a safe and secure working environment and since testing has begun our players and medical staff have done a brilliant job in very difficult circumstances.
"Although we will never be complacent, throughout our own club testing programme, our squad has returned around 2,000 individual negative tests since the outbreak of the pandemic, with not one positive test.
"The current situation has presented huge challenges for all within football and wider society which we do not underestimate in any way.
"While we apportion no blame whatsoever to anyone, this is now a very difficult position for us and, clearly, for all other clubs. Like all other clubs, we must do all we can to protect our squad and limit the very clear and obvious risks to players.
"Under FIFA regulations, clubs are obliged to release players for international duty.
"We will be maintaining close contact with international associations in order to ensure everything possible is being done with regards to the care and protection of our players. The priority must be the safety of our players at all times.
"For clarification, all members of the Celtic squad who continue to train at Lennoxtown during this period have again ALL returned negative tests yesterday (Friday)."
The statement added: "We send our sincere best wishes to Nir and any other players or staff affected within the Israel squad. We are in constant dialogue with Nir and look forward to him returning safely to the Celtic squad as soon as possible."
Speaking at Hampden late on Thursday night, Bitton had smiled and said he would be in "big trouble" with Lennon if he was not fit to face Rangers.
"Obviously Rangers is a big game but I'm not thinking about Rangers right now," he said.
"I don't know if I will travel with the team for the next two games, it is a decision to be made by the coach and the medical staff.
"I gave everything to take part in this game, this is a game that really was my target.
"I didn't really think about the Czech Republic or Slovakia, I only thought about Scotland. So I don't know what is going to happen, we will see."
Celtic have another player, Hatem Abd Elhamed, in the Israel squad.