Despite supporters still being on a high from Cardiff, The Owls skipper knows that if the club do not bring in new blood before the start of the season - it will be a struggle for them to stay in the division.
Paul Sturrock has already signed John Halls and Drissa Diallo but he has made it clear that they will not be the only new additions to the squad this summer.
Bullen told Footymad: "I would say that four or five players at least need to come in. We have just signed John and Drissa but we are still about five bodies down from last season and we definitely need more competition for places.
"At times last season with injuries, we didn’t really have that competition when it was required but hopefully he will get that sorted out. He (Sturrock) is bringing in a few trial players and in a few weeks time we should have everything in place.
"The danger is if we get injuries and suspensions and we have to draft in inexperienced youth-team players into the squad, we could maybe get away with it a little last season but this season with the teams and squads we are up against we won’t get away with it and that’s the reason why we have to bolster the squad.
"The transfer window will have a massive effect. At this level, outside the Premiership, you have to be very careful with budgets and your hand can be forced because you are getting to the last week of the transfer window. It isn’t nice for a manager in that situation and the club but at least everybody has to endure the same problems as we may have in the market."
Coming up tomorrow, the first of a two-part interview with Wednesday's most improved player of last season.