No one wants to face the truth yet but an Achilles tear is very, very difficult to recover from, the mobility in your foot never comes back. Imagine having a foot that it's flexible in certain directions.
Some of the best up and coming players in recent years have had their careers effectively ended at this level due to this injury, Loftus-Cheek, Hudson-Odoi, Koscielny, Johnathan Walters and John Barnes.
I really hope Martinez's isn't that injury or if it is, it isn't severe otherwise he could be in massive trouble. He might also be alright eventually if it isn't his dominant foot.