The Cubs returned Estrada to Triple-A Iowa on Thursday.
Estrada and fellow reliever Brendon Little were both added to the 40-man roster and 26-man active roster as replacement players earlier this week, when starters Justin Steele and Adrian Sampson were placed on the restricted list for the Cubs' series in Toronto. With both Steele and Sampson now having been formally reinstated, Estrada will lose his spot on major-league roster, but he'll remain on the 40-man roster since Chicago selected his contract. He made his MLB debut in Tuesday's 5-3 loss, striking out two and working around a walk in a scoreless inning out of the bullpen.