For anything non-trivial (read: more than around 10-20k SLOC of C or equivalent; straightforward with minimal branching logic; non-critical) you cannot, in any practical sense, have CI without automation. Unless, of course, you want a garbage system. If you do the minimum things necessary to ensure the system is correct (in both verification and validation senses) and of decent quality, and you have no automation, you will not have CI because you will introduce delays between code change and deployment ranging from days (for smaller projects) to weeks or months (for significant projects). That delay means you do not have CI. And it also encourages batching many changes together so that you only have to have one test run (or a small number of test runs) which is also the opposite of CI.

Now, you could bypass all those tests and reviews and just deploy it anyways. And then you'll have a shitty codebase, but you'll have CI so that's good, right?