Ukraine's reigning champion Shakhtar Donetsk, already with a mountain to climb, comes into its Champions League return with Spanish giant Barcelona on the back of a home league loss whereas its rival continues to lord it in La Liga.

Barca's weekend success over Almeria ensured that its stylish 5-1 first-leg home thumping of Donetsk did not distract it from the additional task of keeping Real Madrid at arm's length.

Should Barca now complete the job it will earn another opportunity in the semifinals to rub Real's noses in the Catalan club's apparent superiority - motivation in itself to take the return leg ultra seriously.

While Barca was motoring eight points clear of Real in the league, Shakhtar found its hitherto serene progress towards another title suffer a blip with a 1-0 home defeat by Obolon Kiev - although the leader still has a healthy 11-point cushion over Dynamo Kiev.

The surprise reverse, courtesy of a goal from Obolon substitute Sergei Kucherenko, was Shakhtar's first at the Donbass Arena since the 51,000-seater arena was opened in September 2009.

Although Barca coach Pep Guardiola has publicly warned there is work to do in the second leg he nonetheless has taken the opportunity to call in some fringe figures in the shape of B players Thiago Alcantara - on target against Almeria - Andreu Fontas and Jonathan dos Santos.

Even so, their call-up is largely out of necessity as the Catalan giant, European champion in 1992, 2006 and 2009, must do without injured trio Eric Abidal, Carles Puyol and Bojan Krkic, while midfield general Andres Iniesta is suspended, hence the need for some fine-tuning.

Striker Pedro said on Sunday that the team would not let up in spite of its first-leg lead.

"The team is in good form and winning games. We will not change the way we play. We will concentrate on the job against Shakhtar," said Pedro, while noting that "a tough month lies ahead" as the season enters its final furlong with major prizes beginning to swim within reach.