Celtic face a tough task against PSV Eindhoven or Galatasaray if they beat Midtjylland in the second qualifying round.
Rangers were seeded for the third-round qualifying draw and face a trip to Sweden or Finland for the first leg on August 3-4, with the return at Ibrox on August 10.
Malmo will host Helsinki in the first leg of second qualifying round on Wednesday.
Celtic face Midtjylland at Celtic Park on Tuesday before the return leg in Denmark on July 28.
Rangers have reached the last 16 of the Europa League in the past two seasons, while Celtic were knocked out at the group stage last season after reaching the last 32 the previous year.
If Celtic are knocked out of the Champions League by Midtjylland, they will play Czech Republic side Jablonec in the Europa League.
St Johnstone will play the losers of the PSV-Galatasaray Champions League clash in the third qualifying round of the Europa League.