If an interviewer makes a case like this, you should try to better understand the context. If no additional context is provided, I would try to solve the case by making assumptions on key variables characteristing market entrance and discuss different scenarios.
For instance, consider these 2 variables:
- Client market share
- Type of market entrants
- The client is market leader vs minor player in the market
- New entrants are large corporations growing by adjacencies vs new emerging startups testing a new business model with strong traction
By mixing these factors, you could already build 4 scenarios and provide a structured answer to the interviewer.