Midfielder McKennie had to be helped from the pitch with nine minutes remaining of Juve's 1-1 Champions League draw.
Reports after the game suggested the former Schalke man had fractured two bones in his left foot.
Juve manager Massimiliano Allegri was still waiting on official confirmation as he faced the media, saying: "He is going for an X-ray to his foot; we hope it is nothing serious."
An extended period on the sidelines would prompt concern for both club and country.
While Juve is battling for a top-four finish in Serie A and hoping to advance in the Champions League, the USMNT has vital World Cup qualifiers against Mexico, Panama and Costa Rica next month.
McKennie's international team-mate Giovanni Reyna left Borussia Dortmund's most recent match through injury.