“President Murphy, when announcing the deal yesterday, named only Slapnicka, saying the other player would be named later.” “Fred Clarke and Bresnahan Block Deal for Chic Gandil,” Chicago Tribune, December 16, 1911, p14
“Evers sen[t] the Red president a telegram in which he said he would accept Mitchell and Kinsely, outfielders, Phelan, infielder, and one other player to be named later for Tinker, the Cub shortstop.” “Johny Evers Wants Too Much,” Paterson (NJ) News, November 19, 1912, p6
Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
Although the wording does not exactly match the modern usage, the concept was in use as far back as 1915: “The Baltimore Club has traded Bill Bailey, the southpaw pitcher, to Chicago for pitcher Dave Black and a pitcher yet to be named.” (Sporting Life, Sept. 25, 1915; Peter Morris).
