Their 5-0 win over Levante last weekend may have been a triumph for attacking fluency, not to mention Lionel Messi, who scored a hat-trick, but more surprising was the clean sheet, their third in a row in the league for the first time since March.
"We are on a positive run," Gerard Pique said. "We are playing better, conceding less and scoring goals, it's all very positive."
But after Thomas Vermaelen, their fourth-choice central defender, hobbled off with a calf strain, the Barca board moved on Thursday to sign on loan Colombian international Jeison Murillo despite the 26-year-old having played only one La Liga match all season.
Ernesto Valverde had already switched to three at the back after Nelson Semedo withdrew last-minute due to pain in his knee.
And now Vermaelen is expected out for at least a month while Samuel Umtiti, Pique's principal partner, is in Qatar, hoping to find a solution to his own niggling injury to his knee. The Frenchman's return date is unknown.
That leaves Clement Lenglet, who is experiencing a predictably up-and-down debut season, and Pique, who has improved in recent weeks, but started the season off the pace, like a 31-year-old with his sharpest days behind him.
“It can’t be that we concede every game,” Messi said in October. “We have to be stronger defensively. We are following a year when it was very hard to score against us.”
Barca are still three points clear at the top of the table, although 11th in terms of goals conceded and, given Real Madrid have changed coach and Atletico Madrid won just one away game all season, they might have hoped for a heftier cushion.
In the past, Valverde could have looked within for cover but Barca's youth ranks are not as prolific as they once were. Oscar Mingueza, Chumi Brandariz, Jorge Cuenca and Ronald Araujo are all defenders for the club's B team but none, seemingly, are deemed ready to step up.
Instead, the rumour mill has gone into overdrive, with a replacement sought in January ahead of the start of the knock-out stages of the Champions League.
Lyon were the opponents drawn for the round of 16 on Monday and the French side have already proven themselves dangerous against Manchester City in the group stages. Memories remain fresh too of the four goals Barca conceded against Roma on their way out of the quarter-finals in April.
Valencia's Jeison Murillo, the 26-year-old Colombian, appears most likely to come in but he will do well to find his feet straight away. The demands on playing style at Barcelona are unique and most recruits need time to adapt.
The defensive leaks have other sources too, namely in midfield, where Sergio Busquets has sometimes looked sluggish, particularly when team-mates have been caught upfield and opponents pour forward on the counter-attack.
Adrien Rabiot is expected to join from Paris Saint-Germain, where his contract expires next summer, but his arrival would likely come in June not January.
Celta Vigo could prove generous opponents on Saturday, given their tendency is to retain possession and attack. Ninth in the table, they boast the third most goals scored, as well as the fourth most conceded.
There is also Messi, who tends to make light of deficiencies at the back. He scored three and set up two more against Levante to take the Ballon d'Or's fifth best player to 20 goals in 19 games this season. His 34 in 68 last season saw him collect Europe's Golden Shoe award on Tuesday.
"The truth is I had no idea that all this would happen when I started," Messi said.
Real Madrid's involvement in the Club World Cup final in Abu Dhabi offers Barcelona, and the chasing pack, a chance to extend the gap before the winter break.
Atletico and Sevilla are both two points ahead of Real and three off the lead. Diego Simeone's side face Espanyol, who could have gone top last month but have lost five games in a row since. Sevilla travel to 16th-placed Leganes on Sunday.
Fixtures (all times GMT)
Girona v Getafe (1830), Real Sociedad v Deportivo Alaves (2000)
Real Betis v Eibar (1200), Atletico Madrid v Espanyol (1515), Barcelona v Celta Vigo (1730), Athletic Bilbao v Real Valladolid (1945)
Valencia v Huesca (1100), Leganes v Sevilla (1515), Rayo Vallecano v Levante (1730)