Should I tell him

Ellie • 17
Okay so, I really like this guy that plays on my football team and we get on really well and talk via messaging and at training, but I can't tell if he likes me back. He's flirty but never makes the effort to pop up. I really wanna tell him but don't wanna risk loosing him as a friend or teammate. Any ideas on how I can find out how he feels or how to tell him?