The first piece has been rumored to be top defensive catching prospect Austin Hedges, a possible top-twenty baseball talent whose bat has disappeared since his promotion to Double-A in 2013.
Hedges is currently the No. 22 prospect on MLB.com's Top-100, where his hit and power tools continue to grade at 50.
Three other names listed thus far are Class-A 1B Jake Bauers, Double-A RHP Joe Ross, and RHRP Burch Smith. Jim Bowden has been the Padres source on all names, and expects the deal to include five players from San Diego.
Some number of the players received are then expected to be flipped to the Nationals for an intriguing outfielder, right-hander Steven Souza.
After boasting a .421 wOBA and 161 wRC+ in 2013 with the Nationals' Double-A squad, Souza graduated to Triple-A and bested those numbers, with a .448 wOBA and 180 wRC+ over 96 games, including career bests in homeruns (18) and stolen bases (26).
Before the season was over, Souza was then promoted to the major league team for chances at the beginning and end of season, where he accumulated a meager 74 wRC+ across 26 games in April, May, August, and September.
Over on Fangraphs, Carson Cistulli recently projected Souza to the fourth most WAR among prospects up to age 26 for 2015. Souza placed fourth, just ahead of Joey Gallo thanks to a favorable bat, and just behind Jorge Soler.
UPDATE - 12:15 PM
Bowden has removed Hedges from the anticipated trade, which may make the deal a bit more difficult to swallow if a top-flight pitcher like Max Frier or Matthew Wisler.
Meanwhile, Marc Topkin mentions a fourth team may be entering the fray.