With two Group G games remaining a victory for the Hoops would ensure qualification into the knockout stages while eliminating the Portuguese side with a score draw being enough if section leaders Barcelona beat Spartak Moscow.
Speaking at Glasgow airport ahead of the flight to Lisbon, the former Hoops defender, buoyed by the home win over Barca earlier in the month and the away win against Spartak earlier in the tournament, said: "We are in a great position.
"There is more pressure on Benfica because they really need to win the game.
"But it is a difficult game, it's a Champions League match away from home and we really respect Benfica, we think they are a really good side.
"But the confidence is there, we have shown that we can play away from home so why not go out and nick that vital point?
"They are probably going to go all out and win the game and they are going to be strong at home, a good side going forward, well organised but at the end of the day we have picked up a lot of confidence from our away games and we know that if we defend really well we can get something from this game."
As expected, skipper Scott Brown (hip), midfielders Kris Commons (dead leg) and Joe Ledley (groin), and strikers Gary Hooper (hamstring) and Miku (small procedure), all reported for duty.
Forward Georgios Samaras, who came off during the 2-0 Clydesdale Bank Premier League win against Aberdeen at Pittodrie on Saturday with fatigue, is also in the Celtic travelling party.
Left-back Emilio Izaguirre (hamstring), stopper Thomas Rogne (calf) and winger James Forrest (hamstring) remain out.
Mjallby said: "Scott Brown and Gary Hooper are back in contention and Kris Commons and Georgios Samaras seem to be okay.
"Joe Ledley and Miku are back in contention and we have to wait to see how they are tonight when we train."
Celtic are two points behind Barcelona, who lost 2-1 at Parkhead earlier in the month.
Benfica are in third place on four points while Spartak Moscow are bottom with three.