Not an MD, so my opinion should be read with suspicion. But if your doc told you to take it easy, and your knee hurts when you bike, it doesn't sound like you're healed enough to be riding. Riding hard sounds like a great way to injure your knee further, so you WILL need the MRI and WILL be more likely to need surgery (which may keep you off your bike for 6 weeks to 6 months).
But you'll do what you want to do, and deal with the consequences.