The Cubs optioned Thompson to Triple-A Iowa on Monday.
Thompson's demotion leaves the Cubs with 47 players still left in big-league camp as the club looks to pare down its active roster to 26 men ahead of Opening Day. The 26-year-old right-hander will get his first taste of Triple-A in 2021 after he previously made 14 starts for Double-A Tennessee between the 2018 and 2019 seasons.