Middlesbrough striker McDonald keeps Celtic door ajar
The Australia international joined the Teessiders in January when Celtic sold him as they were reshaping under Tony Mowbray but since the manager has been sacked and McDonald is eyeing a potential return.
“That's entirely not up to me," McDonald said in an interview with STV's Sports Centre.
"Football is a funny old game though, never rule it out. To play for Celtic again would be unbelievable.
"It was a tough decision to leave but I felt it was time to move on when you're not really on the same wavelength as the manager."
McDonald has struggled with injuries since arriving at the Riverside Stadium and has not enjoyed the good form he had in the green and white hoops prior to his move.