So far we are only talking about the fact that Martinez will miss all matches in 2023, and these are matches with Lecce and Genoa, and what will happen next is unknown, but I have not seen any mention that the injury is so serious that he will have to miss the Champions League matches with Atletico, I think that by this time he will be able to return to the game. Against a defense like Atletico's, Martinez will be a very useful player.
Yes, it is very likely that Martinez will miss 2 matches at the end of 2023 against Lecce and Genoa, however Inter is still the favorite because Inter still has Hakan Çalhanoğlu and Marcus Turam who Inter can rely on to score goals and win. Moreover, Inter's defense is very strong so it is very unlikely that Lecce and Genoa will be able to beat Inter by breaking through Inter's defense even though Martinez is not in the team.
I hope that the muscle injury suffered by Martinez can recover quickly. There has been no further news regarding how long Martinez will be out, but I hope that Martinez can recover soon and return to strengthening Inter.
With no one having any update about this injury, but good thing is for the Inter Milan at the end of December they are having not tough match and in January their mostly matches are against weaker sides which are giving them good advantage with they can afford to rest his main player for having 100% fitness before big matches which will be good for the player and team as well.
Even most of the time we have no long term absence due to these muscles related injuries but still until we have any update from the club no one can give any news about this Thuram and Arnautovic done good job against Lecce for their win with the score of 2–0.