This is a "get a vet exam" issue. Due to the location and the amount of swelling, soft tissue or even a boney injury is likely. Many horses won't be markedly lame at the walk, but with lameness at the trot and canter you know there is pain involved.
If you are dealing with a soft-tissue injury, any work right now can lead to ongoing issues with this leg so you are better off getting a correct diagnosis and apporoprate treatment plan than trying to save a bit of money and ending up with a chronic lameness.
Licensed Veterinary Technician