It's been reported that NGT48 member Sugahara Riko will be going on hiatus after receiving surgery on her left knee. 

Sugahara injured her knee last year and had been continuing her activities within a reasonable range. She received surgery on January 15 seeking a complete recovery. While she is doing well after surgery, it will be about three or four months until she can perform on stage. She plans to continue updating her social networking sites at her own pace.

Source: natalie