It's only need 2 weeks for the injury to be recovered, while the match Atletico Madrid vs Inter will happen in the next three months lol. There's no need to worry, it's still long to go and we don't know what will happen next, it could be Martinez suffer ACL injury and make him out from season or it's the other player etc.
Inter doesn't really depend on Martinez anymore, they already have Thuram.
Regarding with some media news I read, Lutaro Martinez not face with serious injury and he will be ready next year or one month before facing Atletico Madrid round of 16. Inter Milan not confirmed yet with Lutaro Martinez need how many week recovery his injury and I think better waiting official confirmation with Lutaro Martinez will absent how many weeks later. Actually Inter Milan is not only with Lutaro Martinez, they have many good players on attacking line Marcus Thuram have quit well performance in this season and Inter Milan with many great attacking midfielder for replacing Lutaro Martinez scoring goals.
If Lutaro Martinez have been absent against Atletico Madrid I don't think its big loss for Inter Milan and Simione Inzaghi will try other option as one striker only with his scheme.