The West Brom midfielder opted out of Saturday's friendly with South Korea, choosing instead to focus on his club's relegation battle as the 'Baggies' find themselves bottom of the Premier League, ten points from safety, with just seven games to go.
Current NI head coach O'Neil gave his thoughts on the decision to the 'BBC': "He won't play in the summer tour and he's a lot to deal with at West Brom as they fight to stay in the Premier League. He knows my thoughts on it - everyone would love Chris to play on.
"If he decides to call it a day, we will respect that. He's been a great player for Northern Ireland and we missed him badly in France to be honest.
"It was a huge blow for him to suffer a cruciate knee ligament injury because he gives us so much in terms of his set-piece delivery and quality general play.
"We hope with a little time away, he's in the right frame of mind to continue for another campaign."
Brunt has made 65 appearances for Northern Ireland, but at 33-year-old, he doesn't have many years left at the top of international football.