The team said Matthew's came down with a fever overnight and by morning was too ill to take his place in the peloton.
"I'm really disappointed to not start this morning," Matthews said. "I've been really ill this morning and tried all I could to make it to the start line, but feeling like this, it's simply not possible. I will now go home to recover and will continue cheering for the guys from there."
Team Sunweb coach Tom Veelers said every effort was made to get Matthews to the start but that proved futile.
"Michael was up early this morning being sick and was unable to keep any food down," Veelers said. "At breakfast, we tried to get some more nutrition into him, but again, he was unable to keep it down."
The defending Green Jersey champion from 2017, Matthews arrived at the Tour without any stated ambition to defend that title and was assigned a designated helper for team leader Tom Dumoulin. Sunweb will now continue with seven riders.
