Although promising around £20million if still in the Premiership, Whelan has guaranteed Jewell he will be given money to spend irrelevant of what league his side are in.
He told the Wigan Evening Post: "The manager will be looking for new players in the summer. We have signed a few players who have been good, a few who have had a lot of injuries, and two or three who the manager hasn't been happy with. As usual at a football club in the summertime, we will have a clear-out.
"Certain lads will be going, and certain new faces coming in. If we can stay in this league, we have to build our squad like Bolton and Blackburn have done, bit by bit, year by year.
"Were we to stay up, we expect to be earning something towards £38million to £40million, and the manager has to get a minimum of half of that.
"All we want to do at Wigan is break even. If we do that we will be happy - we are not looking for profit. The debt we have, I guarantee, so basically we don't have any debt. We've got to strengthen the squad, no doubt about it - the manager will want that and I will support him."