Hellickson, one of the top pitching prospects in the Minor Leagues, will get the start at Tropicana Field, and the rest of the rotation will be pushed back a day. The corresponding roster move to accommodate Hellickson's addition will be announced on Monday as well.
"It's just our attempt at being prudent regarding really monitoring their pitches. It's not about an injury. We just wanted to do this," Maddon said. "It's about having a very capable pitcher like Hellickson, who we feel good about, and throwing him out there in that moment. It's about being comfortable with this pitcher as well as trying to give these other guys an extra day."
Hellickson has been outstanding for Triple-A Durham this season, racking up a 12-3 record and a 2.45 ERA. The 23-year-old will not take anyone's spot in the rotation, as Maddon said that he wants to give his starters some additional rest.
Hellickson left his most recent start for the Bulls after throwing three scoreless innings, but the Rays said his exit was just "monitoring his workload." It is unknown what kind of pitch and/or inning limit he will be on for his debut.
Maddon also said that Hellickson will "probably not" stay with the Rays and pitch out of the bullpen following Monday's start but did not offer any specifics or speculate further on Hellickson's future this season.
"You can make conjecture on that, but probably not," he said. "All I know right now is that we're going to bring him up to pitch Monday."
As Saturday's non-waiver Trade Deadline approached, Maddon and Andrew Friedman, the Rays' executive vice president of baseball operations, repeatedly said that they are confident that their Minor League players can contribute for the rest of the season. Maddon even brought up Hellickson on Saturday afternoon when asked about which players would be able to do so.
"I don't think many organizations have the kind of guys that we have in our own Minor League system that can come up and make an impact," Maddon said. "Hellickson is good, too. Any time you can augment your pitching, that's always a good thing."
Tampa Bay might not have to release or designate any players by the time Hellickson's start comes around, depending on the injury status of Carlos Pena (right foot soreness) and Ben Zobrist (lower back stiffness). If either is put on the disabled list, the Rays can call up Hellickson without releasing, optioning or designating a player on the 25-man roster, although they will have to consider bringing up a position player to make up for the loss.
"There's a lot of kind of nebulous stuff based on Carlos' MRI results and seeing how Zo walks in the door tomorrow," Maddon said.
Adam Berry is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.