McKennie, 22, becomes the second Juventus player to test positive this week, following Cristiano Ronaldo's result announced on Tuesday. Juventus under-23 coach Lamberto Zauli also tested positive on Wednesday.
Juventus play Crotone on Saturday in Serie A (live on ESPN+, 2:35 p.m. ET), and the team will head into "fiduciary isolation," essentially meaning they are heading into self-regulated isolation and trusted not to mix with people outside of their immediate bubble.
"This procedure will allow all persons negative to the controls to carry out regular training and match activities, but will not allow contact with people outside of the group," a statement from Juventus said. "The club is in constant contact with the competent health authorities."
McKennie signed for Juventus over the summer from Schalke on loan and has impressed in Serie A in his two appearances to date.
Meanwhile, Juventus confirmed Ronaldo has returned to Italy after testing positive for the coronavirus in Portugal. He had been separated from the rest of the Portugal group after testing positive for COVID-19 on Monday. He was said to be asymptomatic and in good health condition.
The 35-year-old tested positive two days before the team's Nations League match against Sweden in Lisbon. He was dropped from the squad after another test on Tuesday confirmed the positive result. He had played in the Nations League match against France on Sunday and against Spain in a friendly last week.
No one else in the Portuguese squad had tested positive ahead of Wednesday's match against Sweden.
Ronaldo began his isolation at the team's training centre on Monday. Images published by Portuguese media on Tuesday showed him on a balcony overlooking his teammates practicing at the training centre. In one of the photos, he was shown giving the thumbs-up sign.
Juventus had been in isolation following positive tests for two staff members, but Ronaldo and six other players were allowed to leave and join their national teams.