Check the main pad in his foot. Do you see a callus, or swelling? That is very common in big breeds. It's called bumblefoot. There will be a core in that pad which will have to come out, and it needs to be packed with antibiotic ointment. Cleaned every 2 days, and re-applied until it heals from the inside.
More than likely, but, not always. They have a gland in the bottom of the foot that is hard to see. It can become filled with debris with out seeing it. The only way is to completely clean the foot including the bottom. After cleaning it, you can rub your thumb over the middle pad and open that gland to look at it.
Thank you. I do not think its bumble foot but I will do another check tomorrow. I will bring him in & soak his foot in an Epson salt bath & check it. I have watched several videos on youtube about bumble foot & how to treat it, so I guess I am somewhat prepared.. He walks like a person with a bad knee (I don't know if that helps explain it or not).