Minor League players who are not on the 40-man roster by 11:59 p.m. ET on Friday are potentially eligible to be selected in the Rule 5 Draft.
Fulmer, 22, who was also at Double-A, and Labourt, 21, from Class A Advanced Lakeland, were key acquisitions last summer at the July 31 non-waiver Trade Deadline.
Fulmer, acquired from the Mets in the Yoenis Cespedes trade, tops Detroit's prospect rankings after winning Eastern League Pitcher of the Year honors.