Millwall chairman Theo Paphitis says his side's run to the FA Cup final has boosted the club's coffers by £2.5m.
But Paphitis is cautious about the money-making prospects of playing in next season's Uefa Cup.
Paphitis said: "The FA Cup run is a huge boost to our finances, but we could make zilch from playing in Europe.
"If we go out in the qualifying round against an unknown team we could actually lose money."
A change to next season's Uefa Cup format means teams who come through the qualifying stages will play in a league system.
Paphitis added: "If we come through the qualifiers then we have the opportunity, depending on how far we progress, to make a certain amount of money again."
The Millwall chairman also told BBC Radio Five Live that his promised streak through the streets of London may have to serve instead of players' bonuses.
Paphitis admitted that nobody at the club had thought to negotiate players' bonuses for reaching Europe at the start of the season.
"You only negotiate bonuses once at the start of the season and none of us dreamed Millwall would be playing in the Uefa Cup.
"The boys have been barracking me and I told them if we get into Europe I would streak around London.
"Now they're trying to renegotiate financially but I have told them a bet's a bet."
The Lions are also playing for an even bigger financial stake - a place in the Premiership.
Millwall are well placed in the First Division play-off zone and Paphitis said: "We have a couple of games in hand on people in the play-off places.
"We have a great chance of meeting Sunderland again in the play-offs."
But promotion to the Premiership could see them face the possibility of being expelled from the Uefa Cup.
Under guidelines to come into force next season the coaches of participating teams need to have passed certain qualifications - unless they obtain exemption as a lower league club.
However, Wise does not meet the criteria he must hold a Uefa pro licence, the highest coaching certificate of the national association or have a "recognition of competence" issued by the national association if they have a minimum of five years' experience as a head coach.
Wise only took over as in his first managerial post as Millwall boss in October
2003 and is currently trying to gain his first badge.
He said: "I have not even got a badge, I'm doing the B at the moment. I don't know whether or not you are allowed to manage in the Uefa Cup without qualifications.
"It's not as if I haven't played the game for a few years and I hope to think I know what I'm talking about.
"I'm just finishing the B badge, I hope to finish it in the next couple of weeks. I'm really busy but you have to do it.
"There's certain situations where you need it. It's like taking a driving test, you have to drive properly and I
intend to do it all."