Chelsea head coach Maurizio Sarri held individual inquests after last Saturday's loss to Tottenham and wants answers in Thursday night's Europa League clash with PAOK.
The Blues have won all four of their Group L games to date, including a 1-0 win in Greece in September, to advance to the last 32 and need just one point from two games to seal top spot and a favourable seeding.
Sarri will make changes against PAOK, ahead of 10 matches in December and after defeat to Tottenham ended an 18-game unbeaten start to the competitive season.
He had warned of Chelsea's slack starts, but Spurs scored twice in the opening 16 minutes at Wembley.
"Saturday we played very badly, a match without determination," Sarri said.
"We lost one match after three and a half months (but) we played without determination in such an important match.
"If you don't have determination, you have no motivation. If you have no motivation, maybe you don't have clear targets in your mind.
"We have to understand why, especially from the mental point of view. It's very difficult for me to understand why.
"I wanted to understand this. I talk to them player by player. I have a meeting of five or 10 minutes with the individuals."
One player singled out for public criticism was N'Golo Kante, who was rebuked for roaming from his role on the right of midfield.
The France midfielder won the World Cup in the summer and signed a new five-year contract with Chelsea last week.
Playmaker Jorginho is Sarri's preferred option in central midfield and Kante, a Premier League title winner with Leicester and Chelsea in successive seasons, is adjusting.
"For me the centre midfielder is Jorginho or (Cesc) Fabregas," the 59-year-old Italian added.
"I don't want Kante in this position. Kante in the last match wanted to solve the match after the first 15 minutes, but in the wrong way.
"He lost the position, he attacked too much the other box. And I think this one is not one of the best characteristics of Kante. It was only a reaction to the difficulties."
Sarri has encouraged Kante to get forward in matches and his latest comments may appear to be a contradiction.
But he explained there is a time and place for the Frenchman to attack.
"Kante has to stay near to Jorginho, especially when the ball is on the other side," Sarri added.
"It depends on the action. If the ball is on the left we have (Marcos) Alonso, (Eden) Hazard, (Mateo) Kovacic, (Ross) Barkley, so in that situation he has to stay very close to Jorginho."
Hazard is out with an ankle injury sustained against Spurs, but should be back to face Fulham on Sunday.
