The 31-year-old Republic of Ireland playmaker has to undergo surgery due to a hernia problem.
The former Spurs man will miss a vital part of the season for Forest as they look to push on and close the gap on the teams above them. Forest are facing the possibility of having to play without their skipper in key games against QPR and Derby County in the next months. It is a massive blow for the promotion chasing side as they go into the business end of the season without their key man.
Reid, who recently signed a new deal at the County Ground, to keep him at the club until 2016, has been ever present for Billy Davies's side.
The Reds have lost their "most creative and influential player in Andy Reid".Birtles explained.
"Before Reid got injured, you still felt that the injuries were problems Forest could overcome.
"As we said there is a difference between weakened and weak. But losing Reid is a hammer blow, if he is out for any length of time.
"And, while he is only one man, being without him is probably sufficient reason to re-evaluate the situation."
With Nottingham Forest's injury list building, Billy Davies will be contemplating a move in the emergency loan market to help the club after the loss of Andy Reid and to ensure Forest's promotion bid doesn't come undone at the most important stage of the season.
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