The Trotters brought midfielder Jay Spearing in from Liverpool ahead of this season, but wage bills prevented the club from doing similar deals with other players.
The manager told The Bolton News: "We found last year that we just couldn't trade. The reason for that was there were just so many players under big contracts.
"We narrowly missed out on the playoffs by goal difference last year and I tried to buy a couple of players at the time to get us over the line. Craig Davies, Craig Dawson, they were a couple of deals just to get us through and it nearly worked.
"But when you've got a lot of players on good, long contracts and you can't trade, then you can't trade. And I don't think we did enough of that last summer."
Bolton currently sit 17th in the Championship table.