Injury mid-marathon block

So I have just been to the physio and been told I have Achilles tendinitis, I have not been running for just under a week now because of it and have been advised not to run again for another 10(ish) days.

My marathon is 5 weeks away, so I am worried about how I am going to execute reaching my peak week while not ramping up my mileage too quick. Prior to this I had been up at 55km(34 miles) a week.

My plan is to cycle, swim and walk instead in the time I cannot run, completing a long cycle instead of a long run. When I eventually can run it will be short/easy runs.

So my question is if there’s anyone who has been in a similar situation how did you execute this. I’m worried that by the time I’m able to run again I’m going to be due to do a 32km long run and end up injured again.