if it is tendinitis and not a tear I would suggest cross friction massage on the area. It has helped my patella tendinitis in the past. I've had tightness/pain in my forearms before (not sure if it's the same spot you're saying but it sounds similar) and cross friction has helped relieve the area.
Simply take your thumb and rub across the area perpendicular to the muscle/tendon. You can also try pressure release to try to relieve the area.