Belgium playmaker Eden Hazard missed Chelsea's open training session on the eve of the Champions League semi-final first leg at Atletico Madrid.
Chelsea trained at their Surrey headquarters before travelling to the Spanish capital, but Hazard was absent, the club's official website reported.
Petr Cech, who missed Saturday's volatile Premier League home loss to Sunderland through illness, trained as normal. Hazard suffered a calf injury in the second-leg defeat of Paris St Germain two weeks ago, which secured a seventh semi-final appearance in 11 seasons for the 2012 European Cup winners.
Yet he could be risked at the Estadio Vicente Calderon on Tuesday evening after Chelsea's Premier League title challenge unravelled and boss Jose Mourinho saw his 77-match unbeaten home league run end on Saturday as Europe represents the Blues' best chance at glory this term.
Branislav Ivanovic is suspended, meaning Cesar Azpilicueta could be switched from left-back to right-back and Ashley Cole could return. Alternatively, David Luiz could be fielded at right-back, leaving Azpilicueta on the left and Cole in the margins.
Striker Fernando Torres could feature against his former club, if selected ahead of Samuel Eto'o and Demba Ba. Nemanja Matic and Mohamed Salah are ineligible, having played for Benfica and Basle, respectively, earlier in the competition.
Mourinho is returning to Madrid, where he spent three tempestuous years as Real manager. He is bidding to win the Champions League for a third time after successes in 2004 with Porto and in 2010 with Inter Milan.
Chelsea later confirmed a squad of 20 travelled to Spain, including Hazard.
Striker Eto'o, though, was not included due to a knee injury.
Torres, Ba or Andre Schurrle could be deployed as the furthest forward Chelsea player.