My 4-year-old suddenly held up a back leg after playing — can I just wait a few days?

Don't wait a few days — but you probably don't need to panic tonight either. A limp is pain, and the only question is how urgent it is.

He needs to be seen today if the leg is held completely off the ground and stays that way, if it dangles or looks swollen or crooked, if he cries out, or if there was any real trauma such as a fall, a collision or a car. Otherwise an examination in the next day or two is reasonable — with one condition attached.

The condition is proper rest, and most owners underestimate it. That means short toilet breaks on a lead only, no stairs, no jumping on or off the sofa or in and out of the car, no ball, no wrestling with other dogs — for two or three days, not for two hours. If he is not clearly better by then, he needs examining, because the two most common reasons a four-year-old dog of his size suddenly holds up a back leg after play are a partially torn cruciate ligament in the knee and a kneecap that slips out of its groove. Both get worse with continued activity, and neither can be told apart by looking at him.

Things that will genuinely help your vet: take a video of him walking away from you on a hard floor, so the leg can be seen in motion. Note whether he is worse getting up after a rest or after exercise. Run your hands over both knees and compare — one that is warmer or thicker than the other is worth mentioning.

Never give a human painkiller. Several are toxic to dogs, and pain relief also removes the very thing stopping him from wrecking the joint further. Whether he needs imaging or a trial of rest with prescribed pain relief is your vet's call after the exam.