User blog comment:12th Supernova/Chapter 793: Bad News and Bad Translations/@comment-181.166.68.66-20150709132811/@comment-5387880-20150709225959

naah when Luffy learns that they are going after Shanks he will smile and say something along the lines of don't think that the 3 of you can defeat shanks or that he is the one that will defeat him, he's definetely not gonna fight them to protect him or prevent them from fighting him though.

Obviously if Shanks and Kaido fought they didn't go all out.