必要时

• in a pinch
• at a pinch
• on a pinch
• upon a pinch

例句

1. 必要时我可以在周末加班。
   If need be, I can do extra work at the weekend.
2. 医生认为必要时便动手术－－但可能不致如此。
   The doctors will operate if it proves necessary but it may not come to that.
3. 必要时这张桌子可以坐六个人。
   We can get six people round this table at a pinch.