Open water training with injury?

I've been training for an open water swim that is now about three weeks away. It's a 5k swim and I had been training in a lap pool. I finally reached the 5k mark and was feeling ready for the event until I started having pain in my left shoulder. I saw a doctor and he said it is rotator cuff tendonitis. The pain isn't bad, but I've been forced to cut my training down to about 1-2 miles per swim before the pain gets bad (twice a week). I don't think I'm going to be ready at this pace and to be honest, I don't know if my shoulder will hold up at the 5k unless I take a week or two off with no swimming. Does anybody have some advice as to how I can train and keep my cardio up if I were to stay out of the pool for a week or two so I can let my shoulder heal up? I feel I probably can pull off the 5k swim on a healthy shoulder if I still somehow keep my cardio at a level that will translate well to swimming. I'm running short on time and I'm not quite sure what to do. Any advice from some of you crafty veterans?:bed: