Celtic defender Glenn Loovens could be out for six weeks
Celtic could be without Glenn Loovens for up to six weeks after he sustained an injury at training on Tuesday.
And fellow central defender Darren O'Dea is to join Leeds United on a season-long loan.
Dutchman Loovens is understood to have damaged his left hamstring.
The 27-year-old played alongside Kelvin Wilson in the centre of the Celtic defence in the 2-0 victory over Hibernian on the opening day of the Scottish Premier League season.
But he was unavailable for Wednesday's 2-0 friendly defeat by Swansea.
Celtic's website reported that he could be out for up to six weeks, although manager Neil Lennon was more optimistic speaking after the match in Wales.
Lennon thought Looven may only miss three to four weeks.
"It's a strange one," Lennon said. "He came up off the ground and had a bit of a collision in training and felt the hamstring go."
However, Lennon says he will have midfielders Kris Commons and Joe Ledley ready for the trip to Pittodrie to face Aberdeen on Sunday.
Former Cardiff man Ledley missed out on a trip back to Wales after picking up a niggle against Inter Milan, while Commons was forced to leave the field with a toe problem.
Lennon, who also confirmed the switch for Republic of Ireland defender O'Dea, said: "Kris is fine.
"He has had an infection in his toe and the strapping came off and, when they put it back on, it was too pressurised for him to continue, but he should be okay for Sunday.
"Joe had a niggle from the Inter Milan game on Sunday, but he should be fine for Sunday too."
Lennon also says he is no closer to bringing in a goalkeeper, saying: "We have options, but I can't give you anymore at the moment.
"We are no further down the line than at the weekend."