Celtic boss Ange Postecoglou says there is "not going to be a quick return" for forward Kyogo Furuhashi, who remains missing with a hamstring injury.
The Japan international suffered a reoccurrence of the issue in his side's Boxing Day victory at St Johnstone.
With a much-anticipated Old Firm derby looming on 2 February, the Parkhead manager is awaiting "some clarity" on the 27-year-old's comeback.
"We're still looking at a number of weeks at least," he said.
"It's not going to be a quick return. We're reluctant to put a timeframe on it, just for the player himself, I think it's unfair."
Even if Kyogo was to make a return to fitness, there is a chance the forward would be included for Japan's upcoming World Cup qualifiers on 28 January and 1 February - meaning he would miss next month's Premiership tie with Rangers regardless.
The Ibrox side will already be missing Colombia striker Alfredo Morelos for the same reason, while Postecoglou will be without countryman Tom Rogic after his Australia call-up.
The 56-year-old could also lose further bodies, with new Japanese trio Daizen Maeda, Reo Hatate and Yosuke Ideguchi waiting to see if they will be included for the qualifiers against China and Saudi Arabia.
Midfielder Hatate has never been capped and Ideguchi made the last of his 15 appearances in 2019, the same year striker Maeda last played for his country.
"They're all in the frame," he says. "It didn't help that they did well the other night and got worldwide attention. I was trying to keep that hidden somewhere.
"But I'll be delighted if they get selected. They are players that are really ambitious and want to get to the top of the game. That includes with their national team."
While Posetcoglou will have to deal without the influential Rogic for the visit of rivals Rangers, the ex-Australia head coach will hope new signing Matt O'Riley can have a similar impact.
Midfielder O'Riley, a player Celtic identified as a target prior to Postecoglou's arrival, signed from MK Dons on Thursday for a fee believed to be £1.5m.
With changes expected for Saturday's Scottish Cup visit to League 1 Alloa Athletic, the 21-year-old could be in line to feature.
"We're very pleased to get him in," the Celtic boss adds. "He's a player we've scouted for quite a while. I became aware of him when I joined the club in the summer.
"We followed his progress through the first half of this season and he's had a really good season so far. I see some really good football attributes in him and I think he'll fit in well with what we're doing here."