Naholo, who scored 13 tries for the Highlanders in their winning Super rugby campaign, cracked a fibula in his All Black debut against Argentina in Christchurch on Friday night.
The injury has ruled him out of rugby for three months.
Naholo suffered the injury shortly before halftime, when he was tackled just short of the tryline. However, he played on and was not substituted for Colin Slade until the 51st minute.
''He obviously had an outstanding Super rugby season and he was playing pretty well on Friday night in his test debut,'' Brown said.
''For it to be cut short in World Cup year is devastating for him. But the biggest thing is to understand injuries happen - it's how you come back from them.''
Naholo, who also helped Taranaki win the ITM Cup last year, has not been ruled out of the World Cup comnpletely. If he recovers in time, he could still join the team as injury cover in the middle of October.
''He will be pretty keen to get back in time, just in case someone does get injured and he can go over and play some part of it,'' Brown said.
''I thought he played well against Argentina. They were pretty resilient defensively. They tackled really well. Waisake didn't get a lot of space.
''But what he did do, he did really well. I think the All Blacks coaches will be pretty excited with what he offered.''
News that he had suffered a serious injury came as a surprise to even the coaching staff, after Naholo had been standing on the leg on Friday night.
''We are all a bit shocked about it because he was weight bearing on it pretty good,'' All Blacks coach Steven Hansen said.
''But he got back here [on Friday night] and got really sore, so the doctor thought he better have it scanned. And in the scan there is a very fine crack in it [the bone]. It just means three months out.''