Which tendon and which paw? I know in humans tendonitis can take a long time to resolve - I’ve been battling it for a while in my ankle. Mostly all you can do is anti-inflammatories, rest, and eventually physical therapy to aid in a gradual return to normal motion, and even then it can repeatedly flare up on occasion. Both my kids have issues with tendonitis as well (my oldest as the result of surgery for a broken hand and my youngest with a sports injury to her elbow).
Not a strained tendon, but Chloe completely severed the flexor tendon in her rear paw two years ago. As a result, after the injury she was standing very flat-footed on that leg, couldn’t curl her toes at all and we thought she wouldn’t be able to compete again as you can’t have a dog with any sort of limp in the ring. As an experimental technique, we had the foot splinted for 4-6 weeks in the hopes that scar tissue would form and kind of help to hold the foot in a more normal position. Amazingly it worked, and unless you look very closely at how she is standing on it, you would never know she suffered an injury. When she came out of the splint, as it had been several weeks since the injury when we tried it, she hadn’t been using the leg much at all for a couple months, so she had almost no muscle tone left. It took months of physical therapy to rebuild the muscle, but it worked and she is now doing great.