Freddie Ljungberg could be involved in the 2 January Old Firm derby if Celtic can complete a deal for the experienced Swedish midfielder in time.
The 33-year-old has been training with Celtic and boss Neil Lennon said: "He's done very well in the two days we've seen him. I've been very impressed.
"I've seen more than enough to know he would be a good addition.
"Hopefully we can get something done. If he signs he would certainly be in the squad [to face Rangers]."
Ljungberg, who made his name at Arsenal, is leaving Chicago Fire after an 18-month spell in the United States.