Majstorovic, who arrives at Parkhead on a free transfer, becomes Neil Lennon's eighth major signing of the summer.
He played from the start in his country's 3-0 win over Scotland last week.
The 33-year-old centre-half, who has been released by the cash-strapped Greek club, will meet the media at Celtic Park this afternoon.
Lennon is not finished with the refurbishment of his squad.
The Irishman is also expected to complete the signing of Honduras international defender Emilio Izaguirre this week.
Izaguirre arrived in Glasgow over the weekend and is undergoing a medical ahead of a reported £600,000 move.