PA
Saiz was shown a red card on the stroke of full-time in the FA Cup defeat to Newport.
It was first unclear what the Spaniard had done to earn his dismissal.
But referee Mike Dean has since confirmed to Starsport's reporter at Rodney Parade that Saiz was sent off for spitting at a Newport player, who is understood to be Robbie Willmott.
"I don't know, I didn't see it," Christiansen said when asked about the red card.
"I don't know, when I know I will come back.
"If it's right, why he got the red card, it's a problem.
"But I believe that he didn't do it."
REUTERS
REUTERS
Newport seemed to have earned themselves a replay as the clock ticked into the 90th minute but Shawn McCoulsky's late header sparked wild celebrations.
Leeds, sixth in the second tier Championship, went ahead through Gaetano Berardi's ninth-minute strike and appeared to be heading through until Conor Shaughnessy's own goal 15 minutes from time.
After McCoulsky's headed winner, Leeds's day went from bad to worse when Saiz was sent off in stoppage time.
It is the second season in succession Leeds have suffered a humiliating exit in the Cup after losing to minor league Sutton United in the fourth round last time.