McDonald's studs caught United defender Wilkie on the shin after he raised his foot while stretching to make a sliding challenge.
McDonald told the Daily Record: "I find it astonishing that the video review panel will be looking at this when the referee was standing only five yards away from it when it happened. I thought these reviews were for incidents that were missed by the referee during the match.
"Stuart Dougal didn't miss this one. He just didn't think there was anything in it - and Lee's reaction suggests he felt the same way. He even asked me for my shirt at the end of the game. Do you think he would have done that if he thought I had tried to seriously injure him?
"We shook hands and swapped shirts and I even had a laugh with him asking him to do us a turn by beating Rangers in the last game of the season!
"It's only because the tackle has been highlighted on TV and in the papers that the SFA have stepped in. It's become a big deal because the ref wouldn't allow Lee to be treated.
"Yes, I must admit, when you look at the pictures in slow motion it doesn't look good. But in actual speed it was nothing much more than a brush and I certainly did not try to injure big Lee.
"Lee knows I wasn't trying to hurt him and the ref knew it too. That's why I don't understand what this is all about."
McDonald is the second Celtic player to be referred this week after Glenn Loovens' challenge on Rangers midfielder Maurice Edu sparked another probe.
Both players will be available for Celtic's SPL run-in as the review panel will refer the matter to the SFA's disciplinary committee - which will next meet following the end of the season - if they decide either player has a case to answer.
Tuesday night's incident sparked a major row between Dougal and United boss Craig Levein, who criticised the referee's response after being urged to allow treatment to the defender.
Levein, who claimed Dougal told him to "shut up", has demanded an apology from the official.
He told the Scottish Sun: "I would like an apology and I think Lee Wilkie would also like an apology.
"I have no qualms about anybody making a mistake. Everybody makes mistakes in life. If he didn't see the tackle Scott McDonald made on Lee then fair enough.
"But there is no need for him to speak to me the way he did or treat Lee Wilkie the way he did either.
"As far as I am concerned, we both deserve an apology from Stuart Dougal and I will wait patiently by the phone and see if it happens.
"I don't know if I'll get one, but I'd certainly like one. If that happens, would I think better of Stuart Dougal? Of course I would.
"It's like anything. If someone does something but then apologies then, as far as I'm concerned, it's over, it's done. Everybody makes mistakes."
Levein, who branded Dougal's conduct "disgraceful" after Tuesday night's game, may yet find himself in trouble over his comments if the SFA's general purposes committee decide to take the matter further.