Look at page 29 from "Red Rackhams Treasure" - here's the French original: [link] Captain says: "Ow! My lower back!" Tintin says: "Wait, let me massage you"
As we know, Tintin always means what he says and always gets what he wants! Therefore, the Captain really got a massage, and Hergé forgot to draw it! Ladies and gents, I proudly present --- THE MISSING PANEL!
(Of course, a proper massage can't happen on an island. It has to happen on a bed. So here they are aboard the Sirius )
I can't believe Herge forgot to draw this panel, it must've slipped his mind