The Championship side are looking to tie up the contracts of a number of current players, with Miguel Llera, Jermaine Johnson, Giles Coke, David Prutton and Stephen Bywater all being offered extended deals ahead of the new campaign.
Owls manager Dave Jones guided his side to an 18th place finish last season in their return to the second tier, and Mandaric says he is now looking to help them progress further by bolstering the squad.
"I'm looking at around four players. It could be more. It depends on how many of our existing players renew their contracts," he told the Sheffield Star.
Striker Chris O'Grady has been linked with a return to Yorkshire rivals Barnsley, where he spent the second half of last season on loan, and Mandaric hopes his future can be decided soon.
He added: "Barnsley need to make a decision quickly because we need to start to plan our season."