None of your pets are eligible for battle. You might want to make sure that they're well fed and happy!

Hunger: Bloated Happiness: Very Happy Health: 57/57

I don't know what else I'm supposed to do so he can battle. Help please? Thanks (:

Check and see if maybe it's already in a battle?

Did you battle any of your pets recently, they may be stuck and as others have stated, if you battled recently but didn't forfeit the battle, you may want to make sure it's still not in a battle currently.

File a ticket and a UA should be able to unstick them.

Ohhhhhh...O: Thank you very much! Didn't realise I had to withdraw, haha.