I've had similar, she would not put weight on it, and would whimper if you probed it.

I did take her to the vet, and under examination, which the vet said she would most certainly yelp in great pain when she manipulated it, she did whimper but not the show the vet expected in the event of a break. It was decided without x-rays that it was a very bad sprain with bruising. She didnt say anything about watching for infection (I suspect because she knew it wasnt broken) but she did say that these things can take 3-6 weeks to heal to where the kitty is back to it's normal activity.

True enough that's what happened. Five weeks later good as new.

Hopefully your kitty is similarly affected.

Good luck.