I had a recent experience with the same occurring; the backup catcher was inserted as the pinch runner for the injured Duke Sims, but Tony Perez was substituted at C. Fortunately I still managed to pull out the win.
BOTTOM OF INNING 7
SUBSTITUTION at CF: Matty Alou
0 F.Patek 6 Fly Out b-0 F9
1 F.Peterson 6 Pop Out b-0 F9
INJURY: F. Peterson for 2 more games
2 G.Thomas 3 Triple b-3 F9
2 3 J.Hickman 4 Walk b-1 F9
2 1 3 D.Sims 4 HBP 1-2 b-1 F9
SUBSTITUTION at PR: Paul Casanova
INJURY: D. Sims for 15 more games
2 123 T.Gonzalez 4 Strike Out b-0 F9
TOP OF INNING 8
SUBSTITUTION at P: Bobby Shantz (L)
SUBSTITUTION at C: Tony Perez
SUBSTITUTION at 3B: Tony Taylor
SUBSTITUTION at LF: Tony Gonzalez
SUBSTITUTION at CF: Joe Christopher
SUBSTITUTION at RF: George Thomas