Can't Run/Bike - Cardio Exercises?

sex?

(sorry, but someone had to say it?)

Why don't you wait and see what the doc says? You may still be able to bike, depending on what s/he thinks the issue is. I mean, if you think you can use the elliptical, I don't see why biking would be out of the question. See what the diagnosis is, and ASK your doc what you are and are NOT allowed to do. 

I had some success with aqua jogging when recovering from a foot injury (I could still swim and bike, no impact stuff.) The aqua jogging was good for cardio, but no substitution for running. I did my run work out in the pool, I sweated like I was running, but either I did it wrong, or not enough, because when I started running again, I was beat down physically. So, to make a long story longer, aqua running is good cardio.

Good elliptical machine at the gym. If they have a few different types try them out. One may not feel right.

Your aquajog workouts should be longer and a more intense than what the actual run workouts would be. So, if you're sticking to a plan, and the plan calls for a 45-min run, make it a 60-min aquajog with some tougher intervals. The great thing about AJing is that it's no impact so you can do high-intensity workouts all you want without risking injury. Visit my logs from late Jan 2008 - April/May 2008 for sample workouts.

Oh, and swim more. Once a week is no where near enough.