First noticed reasonably large, hard lump on lower leg after injury (gouge taken out of leg) 7 years later, it's still there. could this be a problem?

Not necessarily: It's difficult to say based on the info you provided. As is the lump in the deep muscle, superficial skin or bone. If it's in the bone, it could be related to a bone callus. If its the deeper muscle, it could be myositis ossificans, which is a calcium deposit in the muscle after truama. Skin wise, that could be a hypertrophic amongst other things. Usually are only problems if create pain.

Examination: Have your physician examine the lump for you. If it has not changed in seven years it's a good sign. However your physician could advise you better after examining it and letting you know whether any future follow-up is needed.