Fowler was ranked by MLBPipeline.com as New York's No. 4 prospect, with Mateo coming in at No. 8 and Kaprielian at No. 12.
Fowler (knee surgery) and Kaprielian (Tommy John surgery) are recovering from major injuries, but once healthy, they could potentially make for a strong return for the A's, who were long assumed to deal Gray this summer.
Gray, 27, was drafted by the A's in the first round in 2011, debuting two years later and turning in a 44-36 record with a 3.