Last season's top scorer in all competitions, Kris Commons, is the Hoops hero the Polish champions fear.
Legia are still celebrating the fact the enigmatic Sami - an unqualified success when it came to finding the net in the qualifiers, especially in away games - has parted company with Celtic.
However, Commons, who scored the vital first goal in the second leg of their play off tie against Shakhter Karagandy last season, which saw the Hoops come back from 2-0 down in Kazakhtan to book their place in the group stage, is set to step into the breach.
It can take the 30-year-old midfielder a few weeks to get up to speed. But on the evidence of the improvement in fitness and form between the two legs of the qualifiers against KR Reykjavik, he is moving up through the gears.
Commons struck the crossbar in Iceland and a post in the return leg at Murrayfield.Those were sighters as he found his range.
He knows how important it will be to start well tonight and try to defuse the electric atmosphere the notorious Legia fans generate.
The Pepsi Arena will be no place for the weak of heart. And, as the most experienced player in the Celtic side, Commons is happy to lead the charge.
He knows the stakes are rising with every round they play en route to the group stage, and accepts there is no room for regrets with so much on the line.
Commons said: "The more games we play, the bigger they become. We are two rounds away from getting into the Group Stage, so the interest gets a little bit higher."
However, just as the rewards increase, so do the potential penalties. Losing in this round would see Celtic drop into the qualification race for a spot in the Europa League, a competition where they learned so much three seasons ago.
Since then, though, they have qualified for the Champions League twice, reaching the last 16 two years ago.
That's the rarified atmosphere in which Commons wants to fly once again, but he accepts that, for now, they are a million air-miles away from realising that ambition.
After four Euro campaigns under Lennon, the change of manager has thrown a fresh twist into the annual conundrum of how to make superiority count against weaker opposition when lack of match sharpness levels the playing field.
Rather than waste energy and time fretting over this, Commons is embracing the new regime and the need to adapt to different demands.
The intensive pre-season schedule has provided a getting-to-know you opportunity for management and players.
Commons and the rest of the first-team regulars were allowed to stay at home to recharge their batteries last weekend when a fringe squad travelled to Hamburg to play St Pauli, and he relished the down time.
"Pre-season has been pretty hectic," conceded Commons. "It has been an enjoyable experience, but there has been a lot of travelling and a lot of games. I am looking forward to the normal season getting underway."
One which must have Champions League football at its heart, the first major target for Deila to deliver.
Commons has bought into his ways, and is confident the transition from Lennon to Deila is being made relatively seamlessly.
"The new manager has settled in brilliant," he said. "Training has been excellent, and the tempo is very high.
"He always wants us to train as we play. He wants us to be very aggressive. But the main thing is he wants us to play attacking, attractive football. Hopefully the fans will see that."
For now, in these defining weeks of the campaign, they will settle for seeing winning football
Which is why Commons' goals can be more valuable than ever.
Surprisingly, after scoring the goal which saw Celtic through their qualifier against Elfsborg, then setting the ball rolling against Karagandy, Commons didn't score another goal in Europe last season.
He wants to do better this time around and is confident the new system worked on throughout pre-season will give Scotland's Player of the Year the chance to pick up where he left off last term.
Commons retains his licence to operate behind the main striker and said: "This style suits me. We haven't changed formation, which is in my favour. The manager wants to me to work off just the one striker, so that is benefiting me a lot.
"Obviously, having good quality players around me makes me a lot better."
Keeping the tie alive for the return leg at Murrayfield a week tonight is the No.1 target for Commons and his team-mates..
A clean sheet is another aim, with any kind of lead to take to Edinburgh considered a bonus.
With the backing of the nomadic Hoops support, who turned up in numbers for the Murrayfield match against KR, Celtic can march on into the play offs.
However, it's very much first things first in the Commons play book, so tonight is as far as he is allowing his mind to wander.
"Legia have a great fan base, so it is going to be tricky," is his summation.
Less so if the Commons strike-rate kicks back into life.