Thomas Tuchel said he took Callum Hudson-Odoi off at half-time against Manchester United for tactical reasons but also because he picked up a minor injury.
Tuchel took Hudson-Odoi off against Southampton soon after bringing him on as a substitute.
And he replaced him with Reece James at half-time against United at Stamford Bridge.
But Hudson-Odoi was then seen holding an ice pack against his leg – which seems to have also played a part in the decision to replace him.
Tuchel said he was taken off largely to ensure that Cesar Azpilicueta and James were able to counter the threat of Marcus Rashford on the flank.
“He’s a little bit injured. The reason was tactical and a little injury – a combination,” Tuchel explained at his post match press conference.
“We switched to a back five in defence and covered the wide position from Rashford in between Azpi and Reece.
“It was not an option to use Callum there and that’s why it was a tactical choice.”
Tammy Abraham was left out of the matchday squad – and that was for purely tactical reasons.
“We have 21 strong players and only 18 possible [to be in the squad], so hard decisions,” Tuchel said.
“It’s my job to take hard decisions and this was the decision for 18 guys and Tammy was not in the group.”