I am glad that Sparky's lameness is mild. Still, considering his use of this leg, this suggests that we have a muscle strain/sprain. And if he is a very active dog and is still trying to go upstairs with an active strain, then this may be why it is not settling for him.
Therefore, as long as he isn't overtly painful, we'd want to just monitor him for the next few days. While doing so, we'd want to restrict activity and rest this leg. Specifically, we'd only want to have lead walks into the garden to do his business and then back inside (no stairs, jumping, or climbing on furniture). As well you can use a bit of supportive care to help this settle for him. If he is amenable, you can consider massaging or warm compressing the leg. If you don't have a warm compress on hand, you can make a microwaveable one by filling a sock 2/3rd full with rice and popping it in the microwave for a few minutes (of course, do give it a shake afterwards to distribute the heat and make sure its not too warm before use).
As well, as long his signs are mild, you can consider some supplements to naturally reduce inflammation and support his joints. For example, you can consider supplementing him with fish oil (omega 3 or 6; EPA/DHA) and/or glucosamine/chondroitin. In regards ***** ***** former, these can be helpful as they do have anti-inflammatory properties. In regards ***** ***** we tend to give this at a rate of 20mg per pound of their body weight. And while more a long term option, it could just help soothe his inflammation and get him more comfortable quicker. Furthermore, you can use glucosamine/chondroitin here. These are a nutrient supplement that is available at your vets, pet shops, and health food stores (as capsules, liquids, and even treats). They work to aid joint suppleness by helping cartilage replenish itself and blocking enzyme destruction of cartilage in the joint. Normally we give dogs 300mg glucosamine + 50mg chondroitin a day per 10 pounds of body weight. So, these would be worth consideration for him as well. As well, you can also consider a low dose of buffered Aspirin (More Info/Dose Here) but we'd want to use that with care (since it can cause GI upset) and only use after meals.
Overall, this sounds like a soft tissue strain that isn't settling due to repeated use. Therefore, we'd want to use the above. Of course, if you do and he isn't settling in a few days, then we'd want to follow up with his vet. They can check the leg for any signs of injury or soft tissue inflammation. Depending on their findings, they can dispense dog safe pain relief/anti-inflammatory medication (ie Metacam, Rimadyl, Previcox, etc) to settle any residual strain and discomfort and get his using the leg properly again sooner.
I hope this information is helpful.
If you need any additional information, do not hesitate to ask!
All the best,