The short answer is yes, it is indeed possible to gain muscle when you don’t eat a great deal. Of course, it will be a little more difficult for you to gain muscle if you’re not in a calorie surplus, but it is doable. There are a few different things that you can do to help you to gain muscle on a calorie deficit or calorie maintenance.
The first thing is to ensure that you’re doing your strength training on a regular basis. This will help you to gain muscle on its own, though a calorie surplus can certainly help.
The next thing to do is ensure that you still have a good enough protein intake to allow your muscles to repair more easily. Having a good amount of protein in your diet can help to increase your muscle gain. It is also helpful to spread your protein across the course of the day. Make sure that you have a minimum of 1 meal with around 30 grams of protein. If you follow this advice, you should still see results in the gym, though they may take longer to achieve.