The punch to Michael's experience broke his cheek bone which gave him a long-lasting black eye (and brought on his sinuses to repeatedly run - for this reason the usage of a handkerchief constantly) till he acquired back again to America and had surgical procedures to repair it (Freddie suggests, https://captainbookmark.com/story18753490/considerations-to-know-about-7-reason-why-the-godfather-master-piece