Contreras was optioned to Triple-A St. Paul on Monday, Brandon Warne of Access Twins reports.
The 27-year-old joined the Twins for their weekend series in Toronto while Max Kepler was on the restricted list. Contreras went 0-for-4 with an RBI and three strikeouts during his most recent stint with the big-league club but will head back to the minors after Kepler was activated Monday.