Frank de Boer's men recorded a 1-0 win in the first leg thanks to Arkadiusz Milik's goal.
And an empty Stadion Wojska Polskiego awaits Ajax due to UEFA sanctions imposed on Legia Warsaw for racist behaviour.
Speaking after the first leg, De Boer said he was optimistic about his team's chances of progressing.
"I feel positive, but we need to wait and see," he said.
"But if we play the same game we did in the first half, they’ll have a hard time.
"It's in our advantage that we kept a clean sheet. It’s in our own hands now and we need to ensure we go through.
"I give us a 60 per cent chance, and Legia a 40 per cent chance."
Rudi Garcia's men have drawn three straight matches and need to turn their form around when they visit the Netherlands.
Rafael Benitez's Napoli crushed Trabzonspor 4-0 in Turkey ahead of hosting the second leg.
The in-form Bas Dost's Wolfsburg are 2-0 up heading to Sporting Lisbon, Olympiacos need to overturn a 2-0 deficit when they host Dnipro Dnipropetrovsk and Dinamo Moscow host Anderlecht after a 0-0 draw in Belgium.
