Sunderland chairman Niall Quinn has pleaded with local fans to buy season tickets.
Quinn says they need to start filling the Stadium of Light for Sunderland to make the next step.
He told the Daily Mail: "But I have to be careful too, people might be getting tired of my message. This is the best chance this club has had in the past 60 years, but I have to be tougher now on those staying away.
"There are people out there watching our games in pubs illegally. They have got to buy a season ticket. If they do, then we're sorted. Our security have gone undercover a number of times in the pubs and we counted around 5,000 watching illegally while we're playing at home on Saturday at 3 o'clock. Some pubs brazenly advertise. That's a real problem for us.
"It's not even just about the money, it's about saying this thing deserves to go further. It's up to the city and the region to respond. Remember, it's the club driving the bid for World Cup host-city status in 2018, which will be enormous for everyone. Is it too much to ask?
"Other research we have done revealed that if you let your season ticket lapse, the average amount of games you go to the next season is two. People find other things to do. By the look of it, they're going to go the pub. If they get tired of me saying that, then someone else will have to come in if this club is to go where it wants to go.
"Loyal fans stayed with the team during the winter's bad run and I'm grateful for that - amazing - but there are others out there who need to get back here. They could make all the difference."