Skysports.com understands a number of Championship clubs are ready to move for Michael Stewart.
The Scotland international midfielder joined Charlton earlier this year after he cut short a stint in Turkey with Genclerbirligi.
The 30-year-old, who held talks with Leeds before moving to The Valley, has impressed during his time in South London.
The Addicks have even offered him terms for next season, but that has been rejected.
His agent Carl Thomas of SEG confirmed that a new deal had been rejected, but refused to comment on his future.
"Yes, Michael has turned down an offer that was made by Charlton, but he is very much enjoying playing for them," Thomas told skysports.com.
"Talks are continuing and that is all we can say at this stage."
Despite the talks with Charlton it is understood his form has impressed a number of onlookers, who could be ready to take him on a free transfer.
The likes of Cardiff, Millwall and Barnsley are believed to be amongst the clubs keeping close tabs on him.