Eiichiro Oda has already hinted on who gave Whitebeard the large scar on his chest in One Piece and it's not Shanks or Roger.

Roger and Whitebeard were equally powerful, with unmatched proficiency in Haki. The true strongest pirate of their time was Rocks D. Xebec, not Roger or Whitebeard. The Rocks Pirate crew ...

It must be noted that Whitebeard was already on his last legs at this point in the story. He had a hole in his chest and half of his face blown off, and all of it came on the back of his already ...