Celtic are sweating over Hatem Elhamed as he isolates from the Israel squad after complaining of feeling unwell.
The Premiership champions face Rangers for the first time this season on Saturday but will be missing a number of key players.
Ryan Christie is out after being told to self-isolate as a close contact of Stuart Armstrong, who has tested positive for coronavirus.
Nir Bitton tested positive for COVID-19 on international duty, while Odsonne Edouard is a doubt after also returning a positive test.
Now Elhamed has been told to isolate from the rest of the Israel squad after feeling unwell.
The defender started against the Czech Republic on Sunday night but was told to self-isolate shortly after.
The 29-year-old will not fly to Slovakia with the rest of his team-mates and will have a test on Monday to determine whether he has coronavirus.
If he tests positive it will mean Elhamed is out for the Rangers game, as he will have to isolate for at least 10 days.
Celtic have already expressed frustration over their players potentially being exposed to coronavirus while on international duty.
After Bitton's diagnosis a statement said: "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."
