The first match between the two takes place on 31 October in Glasgow with the return leg at Ewood Park in Blackburn on 14 November.
The other British sides still in the competition - all from England - will fancy their chances of reaching the third round.
Leeds United will play Israeli side Hapoel Tel-Aviv, who knocked Chelsea out of last year's competition.
Fulham were drawn with Dynamo Zagreb of Croatia while division one Ipswich Town face Slovan Liberec of the Czech Republic.
Opposition for British sides:
Ipswich Town v Slovan Liberec
Dynamo Zagreb v Fulham
Leeds United v Hapoel Tel-Aviv
Celtic v Blackburn Rovers
Matches played on 31 October and 14 November.