Blackwell was addressing a fans forum at Elland Road and hopes to complete the transfer despite competition from Cardiff, who are also keen on the midfielder.
"Sean Gregan is one I am after," Blackwell confirmed. "I spoke to him tonight and I believe we have a decent chance of getting him."
Gregan is a versatile player, either in the centre of defence or midfield and would be a useful addition to the current squad.
Blackwell and the United board also admitted they were hopeful of making another signing before the weekend, and that could happen later today.
They did not mention a name but said they were close to completing the signing on Thursday evening.
It is believed that a dispute between the player's current club and his former club over monies owed are what is holding things up.
The boss added: "If I can have the two players in that I want for the game (Derby) then I will do it, if not then I can assure you that I will keep trying to get the right players in to move this club forward as quickly as possible."