McGrath fate "out of our hands"
Leinster forward McGrath could face a citing and disciplinary hearing for his crude challenge during Ireland's 22-21 defeat to the Barbarians at Thomond Park.
The 25-year-old's World Cup place would be in doubt with a ban, as any suspension would start from Ireland's warm-up matches in August.
Ireland head coach Schmidt said he will review the incident in detail, but conceded that McGrath has left his World Cup spot in jeopardy.
"I saw the long-distance replay and it was pretty hard to see," said Schmidt.
"I thought they were looking at Madigan so I was looking at that.
"I haven't had a good look at it.
"It obviously warranted a yellow card and I guess it's a situation where whatever happens is out of our hands.
"I will try to get a look at it when I get back to the team room tonight."
Schmidt confirmed McGrath's actions contributed to his refusal to send the front-rower back into the fray at the end of his sin-bin.
"It was partially that, and partially because we wanted to give Michael Bent a decent run," said Schmidt.
"We don't probably need to know too much more about Jack.
"You don't get too many free throws of the dice at Test match rugby, so this was a chance to get a look at some players, and that's the reason why we left some guys out altogether."
Alex Cuthbert's brace and another score from Zane Kirchner proved enough for the effervescent Barbarians to edge Ireland out at Munster's famous Thomond Park ground.
Ireland hit back through Craig Gilroy, Chris Henry and a late try for Paddy Jackson, but could not quite complete their attempted comeback.
Ulster flanker Henry made an impressive return on his first Ireland outing since a mini-stroke in November.
The 30-year-old proved his heart procedure in recovering from his autumn illness has no effect on his World Cup chances.
Schmidt hailed Henry's impact, confirming he can still fight for World Cup selection.
"I think he's really good in the group," said Schmidt.
"I think he has an infectious positivity about him.
"He's worked very hard and showed a lot of character to get back into the frame.
"I thought it was great for him to finish that try.
"I think he's still working his way back to the top of his game, and this was another step forward.
"He's certainly still in our thinking.
"Part of Chris being there with Jamie was to help Robbie (Diack) who hadn't had a lot of time with us.
"So he was just keeping guys organised there, and evidently he becomes the link with the backline quite often.
"Chris has brought a real discipline to his game, he lives on the edge without going over the edge too often."
Barbarians captain Shane Jennings brought the curtain down on a stellar career for both Leinster and Ireland, victorious in his final game before retirement.
The 33-year-old led a hungry and focused Barbarians outfit, dripping with finesse thanks to the likes of former All Blacks star Joe Rokocoko.
The Barbarians move on to face England at Twickenham on Sunday, with Jennings predicting another strong performance.
"Fellers fronted up, the subs came on and fronted up and that's pretty infectious," said Jennings.
"It was really, really enjoyable.
"I was so fortunate to play against a lot of my friends from my career, and to win this game was pretty special.
"You have to represent the badge properly, and we did it tonight.
"Hopefully the Barbarians can go out and do the same again in London on Sunday.
"I'm pretty happy. I'm like a Cheshire cat to be honest."