The England international, who was a key player last season when Real won the Champions League and Laliga titles, will be sidelined for several weeks, according to club sources.
"Following tests carried out today on our player Jude Bellingham by the Real Madrid Medical Services, he has been diagnosed with an injury to the plantaris muscle in his right leg. Pending evolution," Real said in a statement.
He will miss Sunday's LaLiga clash against Real Valladolid and England's Nations League matches next month against Ireland and Finland.
Ancelotti, who usually talks to the media one day before each Real game, decided to change the schedule so he could hold his final training session behind closed doors at the Santiago Bernabeu stadium.
Ancelotti said his unusual move had nothing to do with Real's drab performance in a 1-1 draw at Mallorca last weekend which left the usually calm and collected Ancelotti fuming at his players' effort.
"It's nothing special, I'm doing it just to test the pitch because it has changed compared to last year. I want the players to try the new pitch to see how they feel there. There is nothing superstitious or anything else behind it," Ancelotti said.
The Italian insisted, however, that he needs a better performance in order to play with four attacking players in Kylian Mbappe, Vinicius Jr, Rodrygo and Bellingham up front and only two conventional midfielders.
"It was a pretty clear game to evaluate, we lacked balance, it's not very complicated. There is a clear solution," Ancelotti said.
"With such an attacking team, the forwards have to work a bit harder. We have tried to fix it with a lot of work this week."
Ancelotti expects a warm welcome by Real's fans for Mbappe's home debut which is expected to be sold out.
"It's going to be a beautiful day for Mbappe, playing for the first time at the Bernabeu wearing Real's jersey... The fans are going to enjoy it a lot, I'm sure of that," Ancelotti said.
