Abscess

I was rushing to get ready for my lesson yesterday because I couldn't get the new lock on the tack room door open.  I remember having a quick thought that Cupid's leg, where he was injured last year, looked a little different like there was a new lump on it.  I was in such a rush I forgot to put his boots on. 
We walk up to the arena, I get on and we start walking.  Everything seemed fine.  Going to the left Cupid felt a little counter-bent and I was having a little difficulty bending him to the inside.  As soon as I asked for the trot it was clear something was off.  Cupid was willing to trot but was uneven.  We tried the other direction and the same.  My trainer thought it was the right front (the leg he had injured).  We stop and the trainer takes a look.  She also thought there was a lump on the leg that wasn't there before, and said maybe he popped his splint.  I always second guess myself - was that there before??  Did it always look like that?  Is there something clearly wrong that I stupidly didn't notice?  I think I feel heat but am I just imagining it?
Cupid was not too bothered by our examination.  If you pressed enough on the lump he lifted his leg, but hard to tell how much it bothered him.  My trainer also looked at his feet and thought maybe he was sensitive on his feet.  The farrier had said on Thursday that he had a little thrush.
We ended the lesson early and I iced his leg and wrapped it and called the vet.  I wasn't there when the vet came out but he called and thought the splint looked "old & cold" and that he was sensitive to the hoof testers.  So sounds like an abscess or hoof bruise.  The vet poulticed and wrapped Cupid's foot and said it might look worst the next day before it got better.  But generally the prognosis is good.