The Catalan side need a point to finish top of Group H after they lost at Ajax in their last match and the pressure is on after they followed that up with defeat by Athletic Bilbao in La Liga.
AC Milan are second on eight points and the Italians play Ajax who are point further back.
"It is very important for us to finish first and I don't think any games are easy," Martino told a news conference.
"Every match has consequences and we need now to be precise and quick on the ball going forward. I imagine most of the game will be squeezed into 30 or 40 metres of the pitch.
"We need to be well organised as well so as not to be caught on the counter by Celtic who are capable of quick breaks."
Barca's form has been affected by injuries and Atletico Madrid have drawn level with them at the top of La Liga but while Lionel Messi, Victor Valdes and Dani Alves are still in the treatment room, the list of absentees is diminishing.
Xavi and Andres Iniesta have both been given the all-clear to face Celtic as has Cristian Tello but they will be without the suspended Cesc Fabregas.
"There have been games where I have thought we have been close to the level I am looking for and others not. We need to have more consistency and then will play our best. The match against Ajax was a step back for us," said Martino.
Neymar again leads the attack against Celtic in the absence of Messi who will not be available until after Christmas and the coach is not concerned about his lack of goals although the Brazilian has scored only four in total this season and none in Europe.
"For a striker it is not just about goals but also how they play in the team and Neymar has all the facets to do well. He has the right attitude and the goals are going to come," added Martino.
"He is not a goalscorer like Leo, who has different characteristics, but the goals will come. Leo has the ability to make it look easy."