Chelsea manager Mauricio Pochettino has confirmed Enzo Fernandez was struggling with illness before the game, which led to his early substitution during Tuesday's Carabao Cup quarter-final win over Newcastle.
On a dramatic night at Stamford Bridge, Mykhailo Mudryk equalised in injury time to force a penalty shootout which saw young goalkeeper Djordje Petrovic save Matt Ritchie's penalty and seal a semi-final spot.
There was concern earlier in the game, though, when Fernandez was replaced in the first half and then Levi Colwill did not reappear for the second half.
Pochettino explained: "Enzo Fernandez was a little bit sick before the game. He tried, he wanted to play, see if it goes well, but it didn't go so well and that is why he came off.
"My perception was Levi Colwill was a little bit tired and we wanted a more offensive player to provide more energy. That was why we went for the option."
Chelsea had gifted Newcastle the opener when a series of defensive errors allowed Callum Wilson to score, but the hosts were dominant thereafter.
Pochettino was thrilled after the game, telling reporters: "I am so pleased. I want to congratulate the player after we conceded when we didn't deserve to concede can affect any team.
"We reacted really well in a game against a very good team like Newcastle. We kept pushing in the second half, made some changes and tried to make some impact.
He added: "I am pleased because when you see the whole squad, the players who were injured or not involved in the game but happy celebrating in the middle of the pitch, it shows we are a healthy group.
"It shows we only need time and our responsibility is to guide them and create the platform to really improve. With time, it is about creating a team to compete, increasing the competition [within the squad] and being where Chelsea should be."
