What Causes Severe Knee Pain And Muscle Tightness After Extreme Activity?

Hello, my husband is 34 yrs old and recently has been having issues in his knee... muscle tightness, extreme pain, shooting pains up to the small of his back. Its worse after no activity such as when he gets out of bed, and after extreme activity such as when he is at work. He went and got an xray yesterday and no they are scheduling him for an mri... They say it may be tendons torn... i need advie on how to make him feel better, he cant work his boss wont let him come back to work at all. We dont use medications but i rub tiger balm and use salon pas pads with very minimal relief