Q: If the status changes directly from 'With Editor' to 'Required Reviews Completed' in three days, does it mean that the paper will be rejected?

Your knowledge of status updates as well as your powers of deduction and analysis are quite noteworthy. Based on the details you have provided, it does seem to be a no-go decision from this reviewer. However, as we believe, one shouldn’t read too much into status updates, also because the final decision – indicated by the ‘Decision in Process’ status – is made by the Editor-in-Chief (EiC), who may well decide to seek/await the opinion of the other reviewer(s). So, you too should wait until the next update/communication. Additionally, journals sometimes reject manuscripts for reasons beyond the novelty and quality of the paper, as you can find out here: Most common reasons for journal rejection

In case of a reject though, as you may know, you could submit to another journal, making changes as necessary. In which case, you may find this ebook helpful: Tips to avoid journal rejection. It’s free. So, that would soften the blow of the (potential) reject. Plus, it will prepare you for future submissions.

Finally, you may also consider submitting your manuscript (updated or the same) to our new AI-powered platform, PubSure. Apart from helping you improve your manuscript (through machine-based checks), the platform allows you to showcase your improved manuscripts to multiple journal editors, one of whom may consider publishing it in their journal. PubSure thus helps you minimize desk rejection. You may learn more about the platform here: PubSure

All the best for the next steps!