The Senegal defender, signed from Nantes on Tuesday after the Premier League champions were repeatedly turned down by Everton in their pursuit of John Stones, will wear Chelsea's number 15 shirt.
But he has been omitted from the squad submitted to UEFA for Europe's premier club tournament.
Eight locally-trained players must be submitted in the 25-man A List squad, or the squad size be reduced.
Chelsea have a Champions League A List squad of 22 players, which includes summer signings Asmir Begovic, Radamel Falcao, Pedro, Baba Rahman and Kenedy.
Bertrand Traore, the Burkina Faso international, has also been included.
The Blues play Maccabi Tel-Aviv, managed by former Chelsea player and Watford boss Slavisa Jokanovic, in their opening Group G game on September 16.
Former Chelsea defender Tal Ben Haim also plays for the Israeli side.
Chelsea next play on September 29 at Mourinho's former club Porto, with whom he won the 2004 Champions League.
The Blues' third game is at Dynamo Kiev on October 20.
Source : PA
Source: PA