Guadalajara are chasing Manchester City attacking midfielder Nery Castillo.
Guadalajara president Nestor de la Torre told the El Universal newspaper a deal could be done in the next 48 hours.
"Nothing is certain yet," he said. "This evening, we could determine something either for the positive or the negative."
Guadalajara face River Plate in Buenos Aires on Wednesday in the first leg of quarter-finals, but Castillo would not play until the second leg on November 6 should the deal go through.
The deal would represent a significant risk for Guadalajara, as Castillo would be unable to play another other games if they are knocked out by River at that stage.
The Mexican club had tried to sign Castillo in the summer.