Middlesbrough owner Steve Gibson claims Aitor Karanka agreed to part company with the Premier League strugglers in a bid to save them from relegation.
Karanka left Middlesbrough on Thursday, but Gibson insists he didn't sack the Spaniard because he was willing to leave of his own accord.
"I know people are cynical when you say that a decision was mutual, but he wasn't sacked. He sacrificed himself," Gibson told the Times on Friday.
Middlesbrough sit in 19th place in the Premier League table after failing to win any of their last 10 games.
That perilous position prompted Gibson and Karanka to end their three years together at the Riverside Stadium.
"He's in a good frame of mind. I think he's relieved. He has been enormous for our club. He has progressed us and he will have learnt an enormous amount from this experience," Gibson added.
"He's got a wonderful future in football. I really think that."
Karanka's assistant Steve Agnew has been placed in charge ahead of Sunday's clash with Manchester United, and Gibson will not make any snap decisions over a long-term appointment with 11 games of the season remaining.
"I've known Steve a long time. He's a very good coach and a very good number two. There's more to him than people know and a bit more steel," he said.
"Steve could be a surprise number one. That may disappoint those people who want glamour and somebody to come in ready-made, a sexy name, but that's not what we need at this point."