Defeats by Ajax and Athletic Bilbao in recent weeks have been hard enough for the club's proud supporters to stomach, but more painful has been the occasional loss of that which the Catalans cherish most: the ball. In September, for the first time in 317 matches, Barcelona finished with less possession than their opponents. It has happened again since, a symptom of the change in the team's philosophy under Martino: his side are still mostly winning, playing the kind of direct football that arguably suits Cesc Fabregas and Neymar, but perhaps not some of the older stalwarts. "We can't compare ourselves to previous seasons," insists Sergio Busquets but, while they are living in the shadow of such sustained success, Barcelona can expect nothing else. "The style is more or less the same . . . it is non-negotiable."
Events on the pitch beg to differ. Against Bilbao two weeks ago, striving for a late equaliser, Martino took off Andres Iniesta and Xavi, a double change which would have been unthinkable - sacrilege even -two or three years ago. And their have been mutterings from the manager about the criticism he has received: if he were Catalan or Dutch, Martino wondered, would he be under the same pressure?
Another defeat against Celtic - who are admittedly unlikely to unsettle the possession-obsessed socios, having just about managed a 27% share at Celtic Park - and failure to top their group would pile more pressure on a manager whose tactics seem disconnected with the wishes of the club's supporters. Anything other than a convincing win tonight is not good enough.
"We know the consequences every match carries at Barcelona," said Martino. "We have to finish top of the group, so we have to win and play well. Above all, we will need to be very precise and fast with the ball against Celtic. We imagine a match that we will play in 30 metres of the field and we will have to be sure to put pressure on them if we lose the ball to prevent counter-attacks.
"We will pay the consequences if we don't put pressure on and steal the ball back when Celtic are going forward."
Martino admits he was deeply disappointed with aspects of his team's display in losing 2-1 in Amsterdam, and he knows his players need to prove that they are capable of gaining revenge for their 7-0 aggregrate defeat against juggernaut champions Bayern Munich, should the superclubs meet again somewhere down the line.
"Of course, we have to improve our performance to feel we're a team with possibilities of fighting for titles," he said. "In the first half against Ajax, I felt the team had taken a step back in our progression. We know what difficulties we can come up against with Celtic."
Martino raised spirits within the camp on Monday by staging a traditional Argentinian-style barbecue for all members of the first-team staff. "Apparently, it was something out of the norm because it hit the headlines," remarked a bemused Martino. "You have a barbecue and even India hears about it. That is not important for me. We had fun together for a couple of hours and it was good. I didn't pay the bill, so I don't know how much it cost. The idea was a group one and we thought it was a good moment to be together.
"Evidently, there are different ways of analysing how united a team is. Some people see the barbecue as archaic, but we feel it did the team good. We talked about the defeats a lot and what was said satisfied me."
With Lionel Messi out injured and Cesc Fabregas suspended, the focus will be on Neymar to work his magic tonight, and Martino hinted that the Brazilian will be played in a central role rather than out on the left of a three-man frontline. Neymar has managed just four goals this season and is behind Messi, Alexis Sanchez, Pedro Rodriguez and Cesc Fabregas in the scoring charts, but he retains the full backing of his coach. "We look at the whole picture - not just goals scored, teamwork or assists," Martino said. "Neymar ticks all the boxes. He may have lacked the final touch, but goals will come."
"Celtic may have nothing to play for," said Busquets, "but we learned last season that playing against them is complicated. It cost us a lot."