Maurizio Sarri has defended his decision to withdraw replacement Callum Hudson-Odoi late on at Watford, insisting the young forward picked up a hamstring injury.
Eden Hazard reached 101 goals for Chelsea as the Blues edged out Watford 2-1 at Vicarage Road on Boxing Day, but the travelling fans reacted angrily when Hudson-Odoi was brought off with five minutes to play.
Academy graduate Hudson-Odoi replaced Pedro in the 43rd minute only to be replaced himself, by Emerson Palmieri, as Chelsea cemented fourth spot with victory on the road.
The Blues fans heavily booed Hudson-Odoi's withdrawal, prompting manager Sarri to placate the supporters with an explanatory injury update.
"He played for the first time in the Premier League this season, he played for 55 minutes, very well," said Sarri.
"We had a little injury with his hamstring one week ago, and 10 minutes from the end he had pain in the same point so we preferred to change.
"I can understand that (the fans' frustrations) but there wasn't another solution, it was too dangerous."
England Under-19 forward Hudson-Odoi had stepped onto the Chelsea bench for the Watford trip with Alvaro Morata still not over his knee trouble despite having returned to training.
Spain forward Pedro's hamstring concern could now leave Chelsea short-handed at the top end of the pitch for Sunday's Premier League trip to Crystal Palace.
The Blues got back to winning ways at Watford following Saturday's frustrating 1-0 home defeat to Leicester, leapfrogging Arsenal and back into fourth after the Gunners' 1-1 draw at Brighton.
Belgium star Hazard again underlined his importance to Chelsea, racking up a league-high direct involvement in 19 goals for the Blues so far this term.
His 10 goals and nine assists in just 18 Premier League matches have kept Chelsea just in touch at the top end of the standings, with Sarri pleased to see his men back on track after their Leicester reverse.
"Against Leicester I think we played one of the best performances of the season in the first half; what was wrong was the reaction to the negative situation, but it can happen," said Sarri.
"We did very well in our approach, and the level of attention and determination was very good for 90 minutes, with continuity.
"So maybe in terms of quality we played better against Leicester but at Watford we played with a great level of application and determination."
Watford midfielder Christian Kabasele was taken to hospital after colliding with the post when Willian struck the woodwork for Chelsea in the first half.
The 27-year-old revealed he hopes he had not suffered any broken bones in a social media update.
"Good morning everybody, hopefully nothing broken but still have big pain," Kabasele posted on Twitter.
"Thank you for your messages, I hope to be back as soon as possible."