[shī lǎo bīng pí]   

师    老    兵    疲    师、兵：军队；老：衰竭；疲：疲乏。指用兵的时间太长，兵士劳累，士气低落。 贬义>

师老兵疲，成语，指用兵的时间太长，兵士劳累，士气低落。

The troops have been in operation too long and soldiers are extremely tired

师出无名    师严道尊    师老兵破    师老兵疲    师出有名