The hosts have a narrow deficit to make up from the first leg, but their visitors will know that there is still all to play for in this one.
Match preview
PAOK fended off the threat of Borac Banja Luka to claim a 3-2 victory in Wednesday's contest at the Toumba Stadium.
A first-half double from Konstantinos Koulierakis put Razvan Lucescu's men 1-0 and 2-1 up, but they were pegged back on either occasion by Sebastian Herrera and Enver Kulasin before William Troost-Ekong decided the game five minutes into the second period.
That snapped a four-game losing streak for the Greek champions since they kicked off their pre-season campaign with a 2-1 win over AEK Laranca.
Coming up next is a crucial clash for Dikefalos tou Vorra in their quest to make it through to Europe's premier club competition for the first time ever.
Having managed just one win from seven away outings leading up to this one, Wednesday's visitors have work to do ahead of a tough assignment on a road.
Borac Banja Luka gave a good account of themselves on their trip to Thessaloniki last time out, despite ultimately being unable to avoid defeat.
Mladen Zizovic's men had their backs against the wall for large spells of the contest and could have easily been blown away but for a combination of defensive solidity and superb counter-attacking play.
Nonetheless, Crveno-plavi will be in good spirits with 90 minutes still left to play in what remains a finely-poised continental tie.
Unbeaten in eight of their last nine matches on home turf, Wednesday's hosts now go in search of a much-needed win in front of their fans four days before domestic action gets underway this weekend.
Borac Banja Luka Champions League Qualifying form:
W
W
L
Borac Banja Luka form (all competitions):
L
L
W
W
L
PAOK Champions League Qualifying form:
W
PAOK form (all competitions):
D
W
W
W
W
W
Team News
Off the back of his double in the first leg, PAOK's Konstantinos Koulierakis is definitely one to keep an eye on.
Tarik Tissoudali could be handed his first appearance for the home side here having recently completed a switch from Belgian side Gent.
Borac Banja Luka's Enver Kulasin will be keen to pick up where he left off after finally opening his account for the season last time out.
Latest arrival Dino Skorup was thrown into the thick of things in next to no time as he made his full debut against PAOK and the Croatian is expected to retain his starting berth.
Borac Banja Luka possible starting lineup:
Kotarski; Sastre, Troost-Ekong, Koulierakis, Baba; Ozdoev, Schwab; Despodov, Murg, Taison; Thomas
PAOK possible starting lineup:
Siskovski; Herrera, Carolina, Meijers, Kvrzic; Skorup, Grahovac; Vukovic, Savis, Kulasin; Lukic