Contreras is expected to join the Cubs on Friday, Ken Rosenthal of FOX Sports reports.
Contreras has never appeared in an MLB game, but he's tearing the cover off the ball at Triple-A this season, slashing .350/.439/.591 in 54 games. Per Rosenthal, the plan is for the Cubs to roster three catchers for the time being, and a corresponding roster move is yet to be revealed.