Assalamun Alaikum dear brother
The Servant songs (also called the Servant poems or the Songs of the Suffering Servant) are songs in the Book of Isaiah in the Hebrew Bible. They were first identified by Bernhard Duhm in his 1892 commentary on Isaiah. The songs are four poems written about a certain "Servant of God." God calls the servant to lead the nations, but the servant is horribly abused among them. In the end, he is rewarded.
Some scholars regard Isaiah 61:1-3 as a fifth servant song, although the word "servant" is not mentioned in the passage.
According to the majority of Hebrew scholars they speak of one and the same servant.
My point here is that if Isaiah 42 is about Prophet Muhammad then the rest of the song is also about him. We just need to dig even more and find out.
The below are the reference to the Four Servant Songs
Isaiah 42:1-9
Isaiah 49:1-12
Isaiah 50:4-9
Isaiah 52-53
The Christian interpretation of the Suffering Servant is not valid since they believe in atoning for sins of others. We need a Jewish interpretation. Below is a link to a Jewish site. It explains the suffering servant and also prove that Christ is not the suffering servant.
http://jewsforjudaism.org/knowledge?filter-search=&filter-types=&filter-document-type=&filter-topics=suffering-servant&filter-featured=&filter-sort=&filter-sort-order=The site is called Jews for Judaism