Leigh Griffiths will be out of action for the rest of July.
The striker suffered a thigh injury at the end of the pre-season trip to Austria and missed the matches against Shamrock Rovers and Alashkert.
Griffiths had an injury interrupted time last season but thought that he had got things resolved when he underwent surgery to deal with recurring calf and hamstring injuries.
Celtic are well covered in the striking positions with Moussa Dembele and Odsonne Edouard but with a series of tough Champions League qualifiers ahead Brendan Rodgers could do with having the option of the former Hibs striker available.
Explaining the situation to The Sun the Celtic boss said: “Leigh, along with Jonny Hayes, is probably two or three weeks away. We’ll know more in a few weeks’ time. It’s really unfortunate for him but that’s how football works.
“For any player, when you miss a period of pre-season it’s always difficult, especially if you’ve worked hard.
“You want to be at a good level and get as much of your fitness in during this period, so it’s unfortunate for any player that’s out.”
The hoops continue their programme tomorrow with the visit of Standard Liege to Celtic Park in a friendly.
While the return match with Alashkert looks a formality Rodgers will use every outing to improve the fitness of his players with the second round qualifier against Rosenborg or Valur providing opposition who are well into their domestic campaign.