Mantiply will undergo arthroscopic surgery to repair some damage in his left knee, Arden Zwelling of Sportsnet.ca reports.
Mantiply was originally expected to start up a throwing program soon, but after receiving a second opinion on his knee, he decided the best path forward would be to undergo a cleanup procedure. An updated timeline for his return will likely be available after the surgery, but manager John Schneider said the operation won't force the southpaw to miss the rest of the season.