Ole Gunnar Solskjaer reportedly pointed the finger at his Manchester United players after their Champions League exit.
United were dumped out by Barcelona in midweek after a 3-0 defeat at the Nou Camp.
It emerged after the defeat that Solskjaer informed his players of his plans to build a team capable of rivalling their La Liga opponents.
But the Sun reports Solskjaer was also critical of his squad and suggested they hadn't done enough.
The defeat against Barca was United's fifth in seven games with the honeymoon period well and truly over for the Norwegian boss.
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It is claimed Solskjaer was sat with his head in his hands in the dressing room and then issued the address to his squad.
The United boss is alleged to have said some of his players were not giving 100 percent - and hadn't done in recent matches.
Solskjaer was appointed permanent boss on March 28 and his side's performances have been sketchy at best since.
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They have scraped past Watford and West Ham at Old Trafford despite below-par performances and lost twice to Barca.
United were also beaten in their only away Premier League game in that time at Wolves .
Next up is a trip to Goodison Park to face Everton , the first of three crucial games in eight days.
United host City in the Manchester derby in midweek before the visit of top four rivals Chelsea .
The Red Devils won 2-0 at Goodison last season but have managed just two wins from their last 10 visits and can ill-afford to drop any more points in their quest to finish in the top four.
