The Blues trained at their Cobham training base on Monday morning before departing for Portugal without Drogba, whose absence was unexplained in the squad list posted on the Chelsea website.
Diego Costa travelled with manager Jose Mourinho hoping to field the striker despite his ongoing hamstring problems which had previously limited his involvement to one game a week.
Drogba, who scored the decisive penalty in the 2012 European Cup final win before leaving Chelsea, started the opening 1-1 draw with Schalke in place of Costa, but the 36-year-old was a shadow of the player who dominated Premier League and European defences for eight years during his first spell.
He is still awaiting the first goal of his second spell at Stamford Bridge, but it will not come against Sporting on Tuesday night.
Costa, meanwhile, has made a phenomenal start to his Chelsea career and netted his eighth goal in six Premier League games against Aston Villa on Saturday.
Ramires (groin) was the only other senior player not among the 20-man squad, with the Brazil midfielder likely out of Sunday's Premier League clash with Arsenal.
Midfielder/defender Nathan Ake travelled as part of the group, as did goalkeeper Mitchell Beeney, with Mark Schwarzer ineligible in Champions League competition.
Source : PA
Source: PA