Barcelona goalkeeper Victor Valdes
Barcelona have stumbled just as the season enters a critical phase but get a chance to return to winning ways and strengthen their grip on top spot when erratic Sevilla visit the Nou Camp in La Liga on Saturday (2100 GMT).
Wednesday's shock 2-0 reverse at AC Milan, when the determined and well-organised Italians snuffed out Barca's normally lethal attacking threat, left Tito Vilanova's side in real danger of an early Champions League exit.
They host the Serie A side for the last 16, return leg on March 12 but before that are at home to Real Madrid in Tuesday's King's Cup semi-final second leg with the arch rivals tied at 1-1 after last month's game in the Spanish capital, reports Reuters.
Barca visit Real's Bernabeu stadium in La Liga four days later with a another league match at home to bottom side Deportivo La Coruna before the Milan showdown in Europe's elite club competition.
Barca have drawn two and lost one in their last five outings in all competitions and lacked a cutting edge against a resolute Milan despite hogging possession in their customary style.
World Player of the Year Lionel Messi, who has netted an incredible 37 goals in 24 La Liga appearances this term and was top scorer in the Champions League the past four seasons, barely threatened and Barca mustered only two shots on target.
While they are flying high in La Liga, the lack of an effective "Plan B" to break down Milan's resistance is something they will need to address if they are to secure a third European crown in five years.
"Physically we were not good," midfielder Cesc Fabregas, who was replaced on the hour after struggling to make an impact, told reporters.
"They were strong and they caused us damage," the former Arsenal captain added.
"We have to improve and focus on the return leg and on a week coming up now which is crucial for the season."
Sevilla's form has picked up since they sacked coach Michel last month and replaced him with Unai Emery and they still have a chance of qualifying for Europe next season.
The Andalusians are 10th on 32 points from 24 matches, five behind sixth-placed Real Sociedad, who occupy Spain's second Europa League berth.
"We will try to play a good match and get the odd point there," defender Alvaro Botia, who may be tasked with stopping Messi on Saturday, told a news conference on Wednesday.
"They rarely have an off day but that's when you have to make the most of the moment," he added.
With 14 games left, Barca have a 12-point lead over second-placed Atletico Madrid, who host a resurgent Espanyol on Sunday (1800).
Champions Real, whose chances of a second straight Spanish league title were dashed by defeats to rivals including Sevilla, Malaga and Real Betis, play at Depor on Saturday (1900).
Real sit four points behind Atletico in third place.