Check with your doctor to see if it’s okay to swim. Doing the front stroke or back stroke is often okay with an MCL injury, but do not perform the breast stroke as it will stress the knee and exacerbate the injury.
If your doctor does not want you to swim and you can only do upper-body exercise, check for one of two bikes in your gym: An Airdyne or upper-body ergometer. The Air-Dyne has pegs that stick out on the front wheel where you can rest your feet and push and pull with your arms. The ergometer is an upper-body bicycle made specifically for your arms.
-- Sue Falsone