Sampson was assigned to the Diamondbacks' minor league camp Monday, MLB.com's Steve Gilbert reports.
Sampson, who joined the Diamondbacks in spring training as a non-roster invitee, was competing for a bullpen gig, but wasn't able to make enough an impression to claim a roster spot. He'll be stretched out as a starter in the minors, likely serving as organizational depth at Triple-A Reno.