Thank you for the advice and concern everyone!
I had to wake up at 5am this morning, in order to make the 8 hour trip to bring Baby, the Umbrella Cockatoo, and the two Green Cheeks (Salt and Pepper) I rescued to this absolutely fabulous sanctuary where they can live out their lives.
Anyway, I knew it might be good for Chubby to be alone and rest for awhile, he tends to get very excited when we are around and he climbs all over his cage and jumps everywhere. We tried doing the box or aquarium thing but I was afraid he would hurt himself since he kept trying to fly out of it. Anyway, I lowered his perches and bowls, padded his cage, turned on some light classical music, kept the heat up, and had my aunt (who has bird experience) check on him and give him more food twice.
When I left he was still limping and it did not look that much better. Well I just arrived home and I guess he rested all day because now his leg seems fine. He doesn't limp anymore, and he doesn't hold it up all the time while standing either. It does seem a tiny bit more swollen than the other one, but not red and nothing horrible. Like I said, he walks completely normal on it now. He is also eating normally and is happy to see us

So I guess, long story short, it may have just been a sprain or some other minor injury? I'm keeping his perches low and cage padded maybe another day or so to make sure.
"She was not quite what you would call refined. She was not quite what you would call unrefined. She was the kind of person that keeps a parrot." - Mark Twain