Celtic defender Gary Caldwell has apologised to David Fernandez following their collision that has seen the Spaniard face 10 months out.
David Fernandez lies in agony following Caldwell's tackle
"I'm really sorry about what happened, as I've told David, and the fact he was so badly hurt," Caldwell told the official Celtic website.
"I have never gone in to hurt any player in my whole career.
"I got a wee touch on the ball and unfortunately my momentum carried me into him."
Fernandez was strechered off, with what has now been confirmed as cruciate ligament damage, near the end of the first half of Sunday's game.
"These things can sometimes happen in football but it was definitely an accident," said Caldwell.
"I have played against David before.
"He is a fantastic player and a great guy and my fingers are crossed that everything is OK when he gets his scan."
Celtic came from a goal down to beat Killie, who had gone ahead through Fernandez's replacement, Colin Nish, thanks to goals from Shunsuke Nakamura and Kenny Miller.
Fernandez, who moved to Rugby Park from Dundee United before the transfer window closed in August, was due to find out the extent of the damage on Monday.