Ask him how to use a certain piece of equipment or get on a treadmill next to him and say hello. Or ask him if he goes to any of the personal trainers at the gym and can make a recommendation (even if you have no intention of going to one - it just gets conversation started)..
He might not have approached you because he might be unavailable or uninterested but if you start out with something simple and try to start a little conversation, you'll be able to guage his interest fairly quickly by his response..
Edited 4/23/2008 4:40 pm ET by vexer_hw.
Guys always like to feel they're of help. Maybe you can ask him about a particular piece of equipment or a comment about if he's taken a class the gym gives, it sounds interesting... In other words just start a casual conversation about something you obviously have in common. Good luck.
If he likes you, he won't be annoyed if you approach him, he'll be excited...
Absolutely. Friendly and casual is totally the right tone to project.