But despite admitting Celtic's "disappointing performance on the park" is responsible for a dramatic drop in turnover and increase in debt, Reid is adamant Mowbray will continue to have his full support.
He said in the Herald: "I understand the frustrations of supporters and the anxieties they feel. Like them, I want us to win every game we play. But rebuilding the team takes time and right now we are in a period of massive change.
"Supporters generally want rebuilding and success on the field at the same time. And I'm just the same. But Tony has the right to expect our loyalty and moral support while he faces this huge challenge.
"So we will back the manager both with our moral support and with the resources that are necessary to ensure the longer-term success for the club.
"We feel we owe it to Tony to give him loyalty and backing during this time. The rebuilding task is huge but, as I've said, it is all about ensuring the longer-term success of Celtic on the field."
Chief executive Peter Lawwell added: "It is a huge project turning a football club around. It is a long-term project and it takes time and a strategy."
Mowbray was allowed to recruit eight players during the January transfer window.
Lawwell said: "We invested heavily in the summer, too. Basically, in every transfer window, the objective is to come out of it stronger than when we went in. We have a financial strategy that is working and allows us to support the manager in his rebuilding plans."
Asked if the club would spend in the summer, he said: "The strategy will continue. As I say, we want to rebuild the club."
Scottish Premier Winner 2009/10 Win Outright: Celtic 7/2