Degenkolb provided the American team's highlight at last year's Tour, winning in Roubaix on stage nine, while that same day Porte crashed out before the peloton had even hit the cobbles, suffering a broken collarbone.
The 30-year-old told German news website Radsport News: "As it stands now, I will not be riding the Tour de France this year.
"[It is] a decision that I fully accept, because as I said earlier what is good for the team and their goals is good for all of us."
Richie Porte will be looking to better his fifth place finish in the 2016 Tour de France, having crashed out on stage nine of both the 2017 and 2018 editions. He will be riding his first Tour for Trek-Segafredo after making the switch from BMC for the 2019 season, a team he'd raced for since 2016.
The Australian is currently preparing for the Tour at the Critérium du Dauphiné, where Porte sits in 14th place, 1-38 down on Jakob Fuglsang (Astana), after he lost 46 seconds on stage seven's mountain top finish.
There is some hope for Degenkolb, though, as the decision is not completely firmed up and anything can happen between now and July 6 when the Tour rolls out from Brussels.
"The final decision has not yet quite fallen," the German said, "but after six consecutive participations, not going there this year is for me to get over."
At present Richie Porte is set to be joined by a squad of strong climbers who will be able to support him in the mountains, with Trek-Segafredo's provisional squad containing Bauke Mollema and the king of the mountains classification winner at the Giro d'Italia 2019, Giulio Ciccone.
The rest of the provisional squad lists Jasper Stuyven, Michael Gogl, Koen de Kort, Toms Skujiņš and Edward Theuns as set to be making the trip to France come July.
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