Michael O'Neill says he "maybe underestimated" the demands of juggling head coach duties at Northern Ireland and Blackburn Rovers after steering the club to safety in the Championship.
O'Neill took interim charge on a deal until the end of the season at Ewood Park in February with the club 22nd in the Championship table.
Last month, he also led Northern Ireland into the country's World Cup play-off against Italy, losing 2-0 in Bergamo.
But after securing Rovers' second-tier status for another year with victory over Sheffield United on Wednesday night, he admitted he has a decision to make about his future.
"You can't do both, there's no way you could do both because I was only able to do the two things because the [play-off] game was in March, there's no way you could do it when the games are in September, October, November, it's just… it's not possible," O'Neill told BBC Radio Lancashire.
"It was tough enough to be honest and I maybe underestimated that a little bit but I was fortunate I had a really good staff at Northern Ireland.
"The team was extremely well prepared for the Italy game. Unfortunately we didn't get over the line in that game, but at some point I'll have to make a decision one way or the other."
- Blackburn ensure survival with victory at Sheff Utd
O'Neill's contract with the Irish Football Association (IFA) runs until 2028 and he says there will be talks with Blackburn about his future.
He will lead Blackburn into their final Championship game of the season against already-relegated Leicester on 2 May.
"Look, of course those discussions will take place, you know the club have a decision to make themselves, on what direction they want to go," he said.
"I'm a contracted manager, so the situation doesn't really change from, I suppose for any club, if they wanted me as a manager, they would have to go through the IFA, they would have to meet the terms of the release clause and I would have to want to do it.
"That's existed at any point of my management career at international level and it's the same now.
"This was a loan, I suppose given where we are it'll be deemed as a successful loan. I've enjoyed the club, there's a lot of really, really good people at the club and you know. I'm sure conversations will happen one way or the other obviously in the weeks ahead."
