The Spanish side went down 2-1 to their Dutch opponents in the Amsterdam ArenA, and Martino feels that his side need to ensure that their first-half display is not repeated.
"We all have to reflect on this and think about the difference in intensity we saw out there," Martino is quoted as saying on the club's official website.
"We came with qualification certain and Ajax were still fighting to get through, but we can't allow ourselves to play like we did in the first half.
"The defeat has come at a moment where it doesn't damage us as much as it might have and it will allow us to look back at what has happened."
Despite the defeat, Barca are still through to the knockout stages of the competition.