The Addicks last week had a bid in the region of £500,000 accepted but it is understood coming to a compromise over the structure of the deal is proving problematic. The Sky Bet Championship club have also yet to agree personal terms with the player.
Talks are continuing between all parties but O'Grady's proposed switch the The Valley hangs in the balance.
Charlton, who unlike Barnsley narrowly avoided relegation last season, face competition from other Championship clubs to sign the 28-year-old.
O'Grady was the Tykes' top scorer during the 2013/14 campaign with 15 goals and the Addicks' London rivals Millwall are known to be monitoring developments.
"Hopefully things will get resolved but where we're at is a fee, which is close to what has been reported, has been agreed and dialogue remains ongoing," the player's representative said.
"One club has laid out a set way of how they want things done but at the moment they aren't even close. I'd say, as things stand, it was 50/50 as to whether it will happen.
"Clubs have made offers which have not been accepted so, yes, there is plenty of interest in Chris and he wants to stay at that level (in the Championship)."
O'Grady is half way through a two-year contract at Barnsley having joined the Tykes from South Yorkshire rivals Sheffield Wednesday last summer following a loan spell at Oakwell.