The Colombian was a surprise omission for Gers' William Hill Scottish Cup quarter-final in Gorgie.
However, Gerrard explained the 23-year-old was left out of his squad after returning back late from an agreed trip to his homeland.
Gerrard told Premier Sports: "Alfredo's not with us because of a disciplinary issue.
"He was given permission last week to go to Colombia on Sunday until Wednesday to deal with a family matter, which we supported and agreed to.
"He's reported back 24 hours late from that. Due to that he's failed to report to training on Thursday, which means he's missed a lot of preparation going into this game.
"So I've decided to pick players who have done the full preparation and who are desperate to be here and help us get through to the next round."