I would say Yastrzemski was one of the toughest players ever. The only time I can remember him being hurt was in (I think) the strike shortened 1972 season. He hurt his knee in a collision at home. The first doctor told him he would need season ending surgery, so Yaz went looking for another opinion. He found one (probably also a fan) who told him to rest it. That is what he did, and I believe that was the only time he was ever on the DL.
Yastrzemski was tough and one of my all-time favorites, but Pedroia plays the game harder. Writers, fans, and others sometimes accused Yaz of dogging it. No one will ever say that about Pedroia.