Thomas Tuchel has explained the reasoning behind withdrawing Callum Hudson-Odoi in the second half of Chelsea's draw with Southampton, explaining that he was unhappy with the half time substitute's 'energy' at St Mary's Stadium.
The Blues' winning run under their new boss came to an end on Saturday after a Mason Mount penalty rescued a point for the west London side on the south coast.
Chelsea had enjoyed the greater share of possession in the opening stanza of the game, but entered the half time interval a goal down following a classy finish from Saints loanee Takumi Minamino.
Tuchel wrung the changes at the break, introducing Hudson-Odoi from the bench. The 20-year-old has impressed under the German since his arrival, being deployed at wingback, slightly deeper than his usual attacking role.
However, Hudson-Odoi was withdrawn 31 minutes into the second half, leaving the Englishman frustrated as he begrudgingly made way for Hakim Ziyech.
And Tuchel has explained that the substitution was not the result of an injury but a tactical tweak, with the German unimpressed with Hudson-Odoi's second half impact.
'[It was] hard for him to show his quality and we weren't happy with last 20 metres and he could not put his stamp on this game so we changed the formation' Tuchel explained after the game.
'So we brought in Hudson but with Hudson I was not happy with the energy and with the attitude and counter-pressing so we decided to take him off again as we demand a lot.
'We demand 100% and I had the feeling he was not right in this shape to help us so it's a decision for today. It's a hard decision for players to come on and off but tomorrow it's forgotten and he has all possibilities to start against Atletico.'
Tuchel is renowned as a coach unafraid in making tough decisions, however former Blues star Joe Cole questioned whether the German was correct in withdrawing 'magic' Hudson-Odoi ahead of Tuesday's Champions League clash with Atletico.
'Callum can give you a moment of magic but for him to say he wasn't happy with his energy, that's a bold move from Tuchel and it's a gamble because notoriously the Chelsea dressing-room can be fragmented with the amount of changes they've had,' he said on BT Sport.
'So I just question whether it was necessary at the time to upset a player that's maybe going to play for you Tuesday night.
Maybe he's a managerial genius, Callum starts on Tuesday night and gives the performance of his life. But he's a fantastic young player that will be fuming with that today you saw him walking off the pitch.
'Tuchel's took that decision and I do think it might be a message to his team. It's brave because Callum is not going to be happy with that.'
Cole added that the next 24 hours could be crucial for Tuchel as the former England international expressed uncertainty in how the dressing room would react to the controversial move.
'He's had six weeks to get to know the players and personalities. Next 24 hours is crucial. Next training session how do you address it. Because it's a big thing to bring him on and take him off, irrespective of age or personality it's still a big message.
'You live and die by your messages so how the dressing room reacts to it will be interesting. It's bold you don't see managers doing it that early on.'