Pain in Foot/paw

This is the 3rd time this has happened to Elton. It seems like he gets something in his paw but nothing is found. He was chasing a ball and then screamed in pain and will not put pressure on his right front leg. I have gone through and pressed the padding and can't seem to find anything. I can see the pain in his eyes among the scream of pain and wobbling on one foot.

This happened over Christmas and as if magic it was gone. I think it might be along the lines of a sprain or something. Obviously I should go to the vet. The first time I thought it was something in his paw and by the time of the vet appointment he was fine . I did not want to pay $70 at that time because I thought he stepped on something. I now think it is something more because it's the same paw/leg. I don't want to take him to the emergency vet tonight but will go tomorrow.

His physical exams have been good joint wise (patella and hips ) but that's just with regular vet . Any ideas?

He also has a vet appointment Thursday. He has insurance but i just can't think that it still stepping on something when I don't see blood or feel anything. He has been running before ok. I don't think I'm overreacting but even now he is better than before. Since this has come up a couple of times I have a gut feeling there is something underneath this since it's the same leg.