Two Dublin-born former Celts secured their places in the final qualifying round on Tuesday, with Darren O'Dea and Armstrong Oko-Flex both progressing with their respective clubs.
Former Celtic defender, B Team boss and Player Pathways Manager O'Dea joined Yaya Toure 's coaching staff at Slovan Bratislava this summer.
After overcoming Georgian outfit FC Iberia, Slovan saw off Swedish champions Mjallby in the third qualifying round to set up a play-off meeting with Slovenian champions Celje.
The Slovakian club will be familiar to Celtic supporters after Brendan Rodgers' side thrashed them 5-1 at Parkhead in the Champions League two seasons ago.
Oko-Flex is also one step away from the league phase after helping Bulgarian champions Levski Sofia eliminate a side Celtic know all too well.
Levski were paired with Kairat Almaty and, unlike the Hoops last season, managed to negotiate the daunting trip to Kazakhstan successfully.
A late goal gave them a 1-0 advantage from the opening leg before an early strike in Kazakhstan helped secure a 2-0 aggregate victory. Former Celtic youngster Oko-Flex started both matches, with Levski now facing AEK Athens in the play-offs.
Elsewhere, Bodo/Glimt survived a remarkable tie without new Celtic striker Kasper Hogh, eventually overcoming Union Saint-Gilloise 6-5 on aggregate after extra time.
There was another Celtic connection earlier in qualifying as Luis Palma 's Lech Poznan suffered a dramatic elimination against AGF despite winning the first leg 4-1 away from home. The Danish side subsequently endured a collapse of their own, surrendering a 2-1 first-leg advantage as Azerbaijani champions Sabah hammered them 4-0 in the return.
Celtic, meanwhile, will enter the competition at the play-off stage, with Martin O'Neill's side preparing to host LASK Linz in the first leg in Glasgow next week.
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