The 29-year-old's plans came to light on Thursday (AEST) after the German team unveiled their respective line-ups for the 2020 Tour and Giro.
Matthews, who won the green jersey three years ago, will miss the big loop for the first time since 2014 as he prepares for his third career appearance in Italy.
Sunweb's Tour squad will instead showcase Soren Kragh Andersen, Nikias Arndt, Tiesj Benoot, Cees Bol, Marc Hirschi, Joris Nieuwenhuis, Nicholas Roche and Jasha Sutterlin.
As for the Giro, Nico Denz, Chris Hamilton, Jai Hindley, Wilco Kelderman, Sam Oomen, Casper Pedersen, and Martijn Tusveld all join Matthews for the ride.
