Will I lose muscle memory for a sport if I've been injured for a few months?

I think it really depends on how long you've been playing football since before the injury. Say if you have been playing for a good 6-7 years, then you should bounce back to normal in no time. You may may face issues with stamina and getting back into shape initially, but your muscle memory should stay intact. If you've started playing recently enough for a good chunk of muscle memory to be relatively new, then you may feel that you aren't able to access the same set of skills and techniques. However with a good recovery routine and practice with growing intensity as time progresses, you should be able to get back on the pitch in no time! Hope this helps.