IME, even with a fracture you can usually feel it and there will be some bruising along with swelling.
You can try a sling to see if he will tolerate it, but it's a good idea to wrap/splint and/or stabilize the leg even if you sling him break/fracture mends the best it can. This will likely take a couple of months to heal relatively well, maybe more for a large rooster that is heavy.
If at all possible, it's best to see vet care and have an xray to see if the leg is broken or ....
Here's a splinting manual that you may find helpful
https://theiwrc.org/wp-content/uploads/2011/05/Duerr_Splinting_Manual_2010.pdf