The Scottish champions confirmed that defender Christopher Jullien tested positive for COVID-19 two days after the team returned from their warm-weather training camp in Dubai.
Celtic travelled to the United Arab Emirates on Jan. 2 for a six-day training camp, which Scotland's Deputy First Minister John Swinney said was "not a good idea" amid the COVID-19 pandemic.
A club statement on Monday read: "While all of the other members of the squad and backroom team have tested negative, we have been informed by the authorities that, having been deemed 'close contacts', Celtic manager Neil Lennon, assistant John Kennedy and 13 first-team players will be required to self-isolate on a precautionary basis as required by the current regulations.
"The club would like to thank the Scottish FA, JRG and the Scottish Government for their assistance in managing this case. Celtic will, of course, fulfill its fixture against Hibernian this evening. Clearly we are hugely disappointed, as we know our supporters will be.
"The contacts were identified during the period from Wednesday last week, primarily around flight and team coach travel, during which time Celtic applied the same rigorous protocols used for preseason training camps, UEFA match travel and for all domestic match arrangements in Scotland.
"The reality is that a case could well have occurred had the team remained in Scotland, as other cases have done in Scottish football and across UK sport in the past week."
Jullien has become the fifth Celtic player to test positive with David Turnbull, Odsonne Edouard, Nir Bitton and Hatem Abd Elhamed previously contracting the virus while on international duty.
Second-placed Celtic are 22 points behind Steven Gerrard's Rangers side in the league table but have four games in hand.