负伤 means 'to be wounded' or 'to sustain an injury', but it's a separable verb (离合词): the verb 负 and the noun 伤 can be split by 了, 过, or measure words like 次, as in 负过一次伤 ('have been wounded once'). You cannot simply add a duration or count after the whole word — you must insert it between the two syllables. Usually used in formal or military/combat contexts.