The Rams have already seen two bids rejected while Forest are also reportedly hot on their heels but Holloway is refusing to reveal who is set to secure the 26-year-old's services.
"We are very close to a deal," he told the Blackpool Gazette. "The last thing I want to do is lose him but everyone has their value.
"What you have to remember is that players know what other people are getting paid at this level. Even if we doubled his money, it wouldn't be as much as the two clubs chasing him would offer."
Barker predominantly plies his trade at centre-back although he established himself as right-back at Bloomfield Road after signing from Rotherham in 2006.