Jose Mourinho offered a brutal riposte to Frank de Boer's criticism over his handling of Marcus Rashford, with the Manchester United boss tearing into the "worst manager in Premier League history".
Nobody at Monday's press conference previewing the crunch Champions League last-16 clash with Sevilla could have foreseen the Portuguese publicly eviscerating the former Crystal Palace manager.
De Boer was sacked by the Eagles in September after losing his first four Premier League matches without so much as mustering a goal, let alone a point.
That record was brought up as Mourinho went after the Dutchman, having been irked by the former Palace manager saying it was "pity" for Rashford to be playing under the United boss given his preference for short-term success over player development.
"I read something, some quote from the worst manager in the history of the Premier League," the United boss said.
"Frank de Boer - seven matches, seven defeats [sic], zero goals - where he was saying that it was not good for Marcus Rashford to have a coach like me because the most important thing for me is to win.
"If he was coached by Frank, he would learn how to lose because he lost every game."
Palace lost their first seven games without scoring, though the last three of those came under De Boer's successor Roy Hodgson.
Mourinho's stinging comment came in response to a question that did not even reference De Boer, only whether Rashford would retain his starting berth after a match-winning brace in Saturday's 2-1 comeback win against Liverpool.
The Portuguese did not actually address that question ahead of the return leg against Sevilla, nor did he give a straight answer on Paul Pogba's availability on Tuesday.
The midfielder - who surprisingly started the goalless first leg on the bench in Spain - was injured on the eve of the Liverpool clash and was conspicuous by his absence from the section of training open to the media on Monday.
Mourinho offered no insight into Pogba's injury, just that the club-record signing could be involved against Sevilla.
"(Pogba) did (train) after you left," Mourinho said.
"I don't know (if he can play), we don't know yet, but he trained a little bit after you left."
Mourinho confirmed that Anthony Martial is back in contention after an injury of his own, and that Daley Blind, Ander Herrera, Marcos Rojo and Phil Jones remain absent.
The latter will also be unavailable for England over the international break, with the Portuguese saying Gareth Southgate should only select Jones if he "wants to take him for the medical department because he's injured".
Mourinho was in spiky mood ahead of the visit of Sevilla, repeatedly making self-deprecating remarks about his Champions League triumphs as Porto and Inter Milan manager.
Neither of those victorious sides were favourites for the crown and the Portuguese believes United are outsiders this time.
Asked if he feels he has the conditions to bring a fourth European Cup to Old Trafford, Mourinho said: "Not yet, but when a team reaches the last eight anything is possible.
"Now I have only one name in my mind: it is Sevilla. I know that it is very difficult to go through.
"If we go through to the quarter-final draw, it doesn't matter the opponent - for us or for Sevilla - will always be one of the big names in European football, but we will try."