Playing professional sports is not the only thing in life!
If your son is not showing interest in sports, then let him be. Maybe his real interest and real passion lies elsewhere!
Maybe he wants to be a scientist in a lab, maybe he wants to be a writer, maybe he wants to learn ballet (why ever not?), maybe he wants to dance, maybe he wants to learn to paint, maybe he wants to build things, maybe he's destined to become a chef, maybe he wants to be an actor, maybe he wants to be a doctor, a greenhouse man, maybe a fireman (no, really), maybe he wants to become a chess player, maybe he wants to be a fashion designer, maybe a computer whiz........
Have you tried asking him what activities he would like to do? Have you asked him who he dreams about becoming? Have you tried to help him get into those activities? Maybe when he finds the right one for him, then he will show you, the world, and to himself, what he is capable of. Keep in mind, he is still only 13.
And most importantly, even if he does turn out to be a person who is good at things, who enjoys things, and who is a happy kid, but isn't just 'competitive' , the sky isn't going to break and fall. Be happy that he is a happy person. That is what matters.