The 47-year-old father of four was photographed getting some exercise with a few fellow patients in treatment, going for an hour-long walk to lunch around the L.A.-area facility.
McDermott sported basic gray jogging shorts, a simple white T-shirt and a pair of tennis shoes for the afternoon outing, carrying a healthy juice as he worked up a sweat. The star also appeared to be wearing his wedding ring while having a stoic expression on his face.
The Chopped Canada host voluntarily checked himself into rehab late last week in order to address "some health and personal issues" following reports which claimed he cheated on wife Tori Spelling.
"I am truly sorry for the mistakes I have made and for the pain I've caused my family," the actor said in a statement to E! News, adding, "I am grateful to be getting the help I need so I can become the husband and father my family deserves."
McDermott's rehab entry comes just less one month after the reality star was accused of cheating on Spelling with a 28-year-old woman he met in Toronto in early December while promoting his gig as the host of Chopped Canada.
Shortly after the rumors surfaced, Spelling took to her blog to gush over her "beautiful family" and share a sweet video of her kids opening Christmas gifts, despite a source telling E! News that Tori and Dean were leading separate lives.
The couple was last seen together on Thursday, Jan. 9, leaving what appeared to be McDermott's rehab facility. The two were all smiles and seemed surprisingly at ease together.
Just one day later, Tori took the duo's four kids, Liam, 6, Stella, 5, Hattie, 2, and Finn, 16 months, to Disneyland sans her husband, less than one week before McDermott checked into treatment.
The erstwhile Beverly Hills, 90210 actress was most recently seen running errands around Los Angeles on Friday, Jan. 24, wearing her wedding ring, a pair of large sunglasses and a somber expression on her face.
Since the cheating allegations surfaced, Tori is said to be "focusing on the kids" as the situation is still "very raw for her."