Loomis didn't give a timetable, but said he expected Thomas to return "soon."
"I don't expect him to be on it very long, he's just not quite ready to be full go yet," Loomis said.
Thomas, the 2019 Offensive Player of the Year, missed last season because of an injury that occurred when a teammate rolled up on his ankle in the season opener against the Buccaneers on Sept. 13, 2020.
Thomas returned to play in seven regular-season games in 2020 and participated in the team's playoff run that year, but began the 2021 season on the PUP list following ankle surgery that summer. He was expected to return in the second half of the season, but announced in November that a setback would keep him out for the entire campaign.
Loomis said Thomas hasn't had any setbacks this summer that led to the PUP designation. Thomas has not participated in any offseason practices as he continues to rehab his ankle, but was on the sidelines watching one of the team's open practices in June.
Saints coach Dennis Allen said he spoke with Thomas when the veterans reported to the facility Tuesday.
"I had a great conversation with him today," Allen said. "I like where Mike Thomas is, certainly I'd love there not to be any issues at all, but that's not the nature of what we're dealing with right here. I feel like, and we're all feeling like, it won't be very long before we see him out there on the practice field, and we'll start working him back in and getting him ready for the season."
Thomas is one of a handful of players who will begin camp on the PUP list when the team begins practice Tuesday morning. Defensive end Marcus Davenport will also start on PUP after undergoing the partial amputation of his pinky in the offseason, while safety Tyrann Mathieu has been excused for a personal matter.