Manager Nigel Clough has revealed Derby have made offers for two players and are set to table two more bids this week.
The Rams, who have already signed goalkeeper Frank Fielding from Blackburn and forward Jamie Ward from Sheffield United as well as agreeing a deal for Millwall striker Theo Robinson, are also in talks with several out-of-contract players.
"Offers have gone in for two Championship players and another two offers are going in this week for another two players," Clough told the Derby Telegraph. "That will be four players we are bidding money for.
"At the same time we are talking to the free transfers, of which there are three or four. They are keen to see what is out there and take a week or so just to make up their mind.
"We are working as hard as we can to get these players in. Every player we are bidding for or chasing on a free transfer, bar one, are established Championship players or younger players from the Premier League, which are likely to be loans."