The north London club have never played the Bulgarian outfit, who overcame Iskra Danilovgrad of Montenegro in the previous round.
Rangers, meanwhile, are away to Lincoln Red Imps.
The Gibraltarian side beat Celtic 1-0 in Brendan Rodgers’ first match in charge in July 2016.
However, the Hoops went on to win the second leg of the Champions League second qualifying round tie 3-0 and progress.
The away theme for British teams continues, with Aberdeen travelling to Norway’s Viking.
Motherwell have been drawn against Northern Ireland’s Coleraine, and go into the match on the back of a 5-1 win over Glentoran in the first qualifying round.
Coleraine’s first-round win over Maribor ensured Well edged into the seeded half of the draw.
Coleraine manager Oran Kearney is no stranger to Scottish football, having previously been at the helm at St Mirren.
The Republic of Ireland’s Shamrock Rovers will host former seven-time Champions League winners AC Milan.
The Serie A club will have to travel to Dublin for the behind-doors clash.
Rovers qualified for the second round with a penalty shoot-out win over Finland’s Ilves Tampere last week.
Elsewhere, Bala host Standard Liege, Dundalk were drawn against Andorran club Inter Club d’Escaldes, Connah’s Quay were paired with Georgia’s Dinamo Tbilisi and Linfield will face Floriana of Malta.
The New Saints of the Cymru Premier, meanwhile, travel to Faroese side B36 Torshavn.
All the ties will be single-legged affairs, and are expected to take place on September 17.
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