The precautionary reasons were not immediately clear. He had two shots in 17:23 of ice time during Saturday's pre-season loss to the Toronto Maple Leafs.
Caufield, 20, produced 12 points in 20 games for the Canadiens en route to the Stanley Cup final last season. The five-foot-seven American also played in 10 regular-season games, but will be considered a rookie for the upcoming 2021-22 season.
A 15th overall draft pick in 2019, Caufield won the Hobey Baker Award as the top NCAA men's hockey player last year. He produced 33 goals and 22 assists in 31 games with the Wisconsin Badgers.