Well, it’s not that hard. IMO you definitely can let him know that you have a feeling for him without saying anything explicit about it. Here are what you need to do:
Be visible: This is especially essential if the guy you like doesn’t even know that you exist. If that’s the case, it won’t be good if you will just walk up to him and tell him squarely that you like him. So you have to make him notice you first. “Accidentally” bump into him in the gym or in the library. Don’t forget to say hello when you have the chance. Making him aware of your presence is a nice start to starting a longer conversation in the future;
Be attentive to him: Laugh at his jokes; respond to his questions, essentially giving him your full attention when you’re around him. Guys love to be the center of attention so he’ll appreciate you more if he can see that you are interested in the things he do and say;
Be there for him: Find out what subject he is having a hard time with and offer your help. Always be ready to lend an ear when he needs someone to talk to about his problems. With technology, that’s even easier nowadays. You don’t even have to be physically present just to make him feel that you are ready to listen. Texting, social media, and Facetime can all work in your favor.