Martino invited the entire first-team staff to a traditional Argentinian roast and grill held at the Sant Joan Despi training centre on the outskirts of the city yesterday afternoon to raise spirits in the wake of a disappointing run of results.
The Camp Nou giants battled back from a goal down to win 4-1 against third-tier Cartagena in the Copa del Rey last Friday night, but they are still smarting after a 2-1 Champions League defeat by Ajax and suffering their first league loss of the campaign at Athletic Bilbao.
Bartra insists the lunchtime get-together did a power of good for morale and has warned Celtic that the Catalan giants' recent blip is now well and truly over.
"It was a nice gesture from the coach," said the central defender. "It's important to do things that create team spirit and having lunch with the rest of the team is always good. When complicated times or important times come, you will be more united. Winning the cup game after two successive defeats always makes you feel more confident as well. It was a way of putting our fist on the table and saying that's enough. I am happy with that because it means we can now face the likes of the Celtic match with greater eagerness. We will go with all we have."
Cartagena created two great chances early in that match before taking the lead and Barca had to pull something special out of the hat with two goals from Pedro Rodriguez helping secure the victory along with efforts from Cesc Fabregas and 18-year-old Cameroon forward Jean-Marie Dongou.
Bartra does not believe the team's difficulties should be taken as a sign they are struggling ahead of the final match of Champions League Group H, though, and feels the performance they delivered in an unfashionable and difficult venue proved they have the appetite for a battle when required. "We played against a team from the third tier, of course, and put up a good fight. For a team that has won so many titles, going there and playing the way we did showed our professionalism. Some thought our team could have been down in the dumps, but we were courageous and turned the match around."
Barcelona, and Martino in particular, have been the subject of criticism from the Catalan press lately, something Bartra acknowledges. "We have to realise where we are and we do set the bar very high. We have to continue doing that. We won everything through playing good football and earned people's respect because they value the way we perform as well as the things we win.
"When you are not up to those standards, you know that you are always going to be open to criticism. The best we can do with the criticism is take the positives from it and get stronger. If you can remain mentally strong amid the criticism, you will maintain a good level."
Bartra is desperate to face Celtic and prove his worth as talks continue over a contract renewal. "I am eager to play, as usual, because there are only four matches left until the end of the year and it is important to end the year on a high," he added. "We had come from two defeats before the Copa del Rey match and that victory has given us more confidence. We want to keep winning from now until the end of the year."
Alex Song echoed his team mate's thoughts ahead of the visit of Neil Lennon's men. "It's important we respond well to that defeat and we are determined to play well against Celtic," said the Cameroon internationalist whose side still require a point to secure a first-place finish in the group.
"Barcelona are the best team in the world but, to prove that, we have to win every game. These days, our opponents work so hard during games. We have been self-critical and now we will look forward to better things. Compared to my first year here, I feel better. It takes time to adapt to a new language and culture, but I found a large family that has welcomed me with open arms."