Harps were held to a 1-1 draw in Cork on Sunday, but are quietly confident they can overcome the dogged intermediate side and book a place in the last four.
Campbell believes Harps chances of progression would be boosted if a big crowd descended on Finn Park, but appreciates the timing of the fixture isn’t great.
Campbell told Donegal Daily, “I’d love it if people could make an effort to get to Finn Park tonight and give the lads support for what is an absolutely crucial match.
“A place in the cup semi-final is up for grabs, and they don’t come round too often.
“I know with Donegal in the All-Ireland final on Sunday, people will be trying to save for that, but I hope soccer supporters all over the county make a genuine effort to come out and support,
The last time Harps reached a semi-final was in 1999, they defeated Galway United to set a final meeting with Bray Wanderers.
Campbell believes the management and players deserve a big crowd, and praised their efforts throughout the season.
“The management and players deserve a big crowd, they’ve all put in a heroic effort all season, the effort and commitment has been top class.
“They deserve a big crowd to come out and support them, a place in the semi-final would be fantastic for the club, and hopefully we can get over the line tonight.