Is Exercise Advisable After Having A Ligament Tear In The Knee To Reduce Weight?

hello doctor..good morning my husband is 34 yrs , appx 100 kg of weight and height around 5 10 inches. He had an knee injury last year. his ligament broke of left knee. as adivised by doctor he walked with stick for 4 months but didnot go for any surgery. After leaving stick he used knee belt to walk. now last month only he stopped using knee belt also. i just want to ask that.. Can my husband do any exercises to reduce his weight ? Can you suggest any exercises which do not put pressure on his leg/knee ?