A similar approach for midfielder Michael Brown was rejected by Tottenham, but Blackwell will persevere with his strategy next month with Leeds fourth in the Championship.
He said in the Yorkshire Evening Post: "It's only worth adding to my squad if I can find players who will make a real difference. That's easier said than done because of the quality we have here. It will probably mean concentrating on Premier League players.
"Most clubs in the Premiership have been reluctant to let players go before Christmas, but that will change in the New Year."