Collier made all but one of his starts this season with Class A-Advanced Lakeland, going 5-3 with a 4.43 ERA and 54 strikeouts in 67 innings.
Faulk earned an invitation to big league camp this season, and had a 3.65 ERA over 32 relief appearances with Triple-A Toledo. Faulk held opposing hitters to a .170 average and struck out 52 in 44 1/3 innings, though he had 31 walks.
Hardy split the season at Double-A Erie and Toledo, going 8-3 with a 1.67 ERA in 30 appearances and nine starts. In his last three starts, Hardy tossed 24 scoreless innings, giving up just eight hits and striking out 11.
Machado battled injuries throughout the season, playing 37 games with Lakeland and batting .215 with 19 runs scored and 12 RBIs.
Those four players will join Tigers prospects outfielder Tyler Collins, infielder Devon Travis and right-hander Corey Knebel, who were already named to the team at the end of August.