My Husband's Lower Left Calf, Above The Ankle On The

My husband's lower left calf, above the ankle on the outside of the leg, is red and painful. He has a history of cellulitis about 3 years ago. I'm also concerned that it could be a blood clot. He has no history of clots. The only symptom he complains of is pain. But the leg is red and tender to touch and it feels warm.