Celtic face Benfica in Portugal on Tuesday ahead of a final group match with Spartak Moscow and Mjallby believes that is would be "wonderful" if the club could seal their passage through to the last 16.
Mjallby said: "It would be a wonderful achievement for the players and the management. Obviously we can't compete financially with the other three clubs in the group. So I think it speaks volumes for the players, how hungry they are and their desire to improve all the time.
"No one gave us a chance when the draw was made but we always believed in the players and maybe they did even better than we expected."
Celtic would qualify for the knockout stages if they beat Benfica.