Derby caretaker manager Terry Westley is taking a look at former Millwall midfielder Lloyd Dyer.
The 23-year-old was released by the Lions earlier this month at his own request and has been training with the Rams this week.
Westley told the club website: "Lloyd is out of contract and we can't do a deal with him.
"He will be with us until the end of the season with a view to looking at him for next season."
Derby are unable to sign Dyer because of the transfer window regulations, as he was still registered with Millwall when the window closed in January until he was released.