And there's more. Fast forward to the 1991-92 season. This was Liverpool's first back in Europe after being banned for the previous 6 seasons - all other English clubs copped a 5 year ban but Liverpool were given an extra year - so you'd think their fans would be falling over themselves to get to Anfield for one of those famous "European nights under lights". Anyway, their first home game in that season's UEFA Cup against Kuusysi Lahti attracted a crowd of 17131. To be fair they got over 23000 in the next round against Auxerre but against FC Swarovski Tirol in the 3rd round they pulled in only 16007.
I think it's only fair to compare attendances that other clubs pulled in similar competitions from the same era so the season before that when the ban on all other English clubs was lifted Aston Villa played Banik Ostrava at Villa Park in the first round of the UEFA Cup. Attendance? 27317 - over 10000 more than Liverpool got a season later for their first round home match in the same competition. On the same night Villa were playing at home, United's first round first leg game in the ECWC at Old Trafford had an attendance of 28411.