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John Minchillo/Associated Press

The Cincinnati Reds' starting rotation entered play Wednesday with a fifth-ranked 3.76 ERA, in no small part due to ace Luis Castillo.

The 26-year-old is fourth in baseball in ERA (2.41) and has struck out 134 in 112 innings. He's making a credible case for the National League Cy Young Award and is under club control through 2023.

The Reds are in last place in the NL Central and should be in seller mode. According to Jon Paul Morosi of MLB.com, there's a chance Cincinnati would move Castillo for the right gaudy package.

As Morosi put it: "The Reds haven't hung up the phone on teams who have called. They are waiting to be wowed..."

Let's examine five suitors who could wow them before the July 31 trade deadline, and the prospect packages it might take to reel in one of the most exciting young pitchers in the game.