Celtic have suffered a double blow with the news Scott Brown and Shaun Maloney face extended spells on the sidelines.
Midfielder Brown faces another operation on his ankle injury, while forward Maloney has been struggling with an Achilles problem since the Co-operative Insurance Cup defeat to Hearts last month.
Brown has been struggling with the ankle injury for some time with the club hoping rest might resolve the problem.
The Scotland international visited a specialist in Holland this week to try and get to the bottom of the issue and it has been discovered he requires a new operation.
It means Brown faces a further two months on the sidelines meaning the former Hibernian ace will not return to action until January at the earliest.
Maloney does not require surgery, but will continue to receive treatment on his Achilles injury.
The injuries are a major blow for Celtic as they look to end their current slump in form.
"Scott has been to Amsterdam to see a specialist," said Mowbray.
"We have come to the conclusion where we go now.
"Scott will have a minor procedure in Amsterdam which will hopefully clear up his problem. Ultimately we need to get it sorted.
"The specialist who is overseeing Scott is looking at him being out for six to eight weeks. Maloney is also out for the same length of time. There will be no surgery, just a course of injections.
"He has played with discomfort and he needs to sort it out now."