Thielbar was included in Minnesota's 60-man player pool ahead of summer camp before the 2020 season begins, MLB.com reports.
Thielbar has thrown all 98.2 of his major-league innings for the Twins, though none of those have come since 2015. He's since spent time in independent ball and in the minor-league systems of the Padres, Tigers and Braves. The lefty will likely spend most of his time with Minnesota's alternate training site unless the major league bullpen needs depth.