Scar on his side right belly

I've always noticed that Al doesn't like showing his stomach or belly button, in every shirtless scene, he is covered from the waist down. Despite his small stature, his arms and shoulders seem well muscled, yet he covers himself up always. I was rewatching Scarecrow, and as he was getting out of the shower, and as he grabbed his towel to cover up, I noticed he had a greyish scar by his right stomach, parallel to his belly button. It seemed roundish to me and oddly grey. So I'm wondering if it was makeup and they tried to cover up something already there. The same greyish color can be seen on Al's nose after he was beaten up, to show his bruise. But the grey belly scar was before the beating and Al clearly is trying to cover it up with a towel.

Has anyone seen the film Scarecrow (1973) and noticed this scar? And does anyone know where he might've gotten it from? I'm assuming this is the reason he covers up his waist area in every film.