First baseman Kila Ka'aihue, outfielder Brad Snyder, pitcher Rommie Lewis and catcher Rossmel Perez were all assigned to Minor League camp.
Skaggs struggled this spring, compiling an 11.00 ERA in four appearances. In his nine innings, he allowed 14 hits.
"He just wasn't ready," manager Kirk Gibson said. "We felt it was being counterproductive him being here. I think he was a little bit relieved, to be quite honest with you. We'll get him back on track."
Patrick Corbin and Randall Delgado will now fight for the final rotation spot.
Gibson said he thought some of Skaggs' struggles were the result of him putting too much pressure on himself in trying to win a spot. That led to some mechanical issues, and in turn, command problems.
In nine innings, Skaggs walked eight and struck out five.
"If you can't command your fastball, it's not going to cut it," Gibson said. "He knows what he has to do. We'll get him down there, we'll get him on track, he'll make some adjustments and hopefully he'll relax a little and throw the baseball the way he's capable."
Steve Gilbert is a reporter for MLB.com. Follow him on Twitter @SteveGilbertMLB. This story was not subject to the approval of Major League Baseball or its clubs.