The agent of Hibernian's Kevin Thomson and Scott Brown claims the club have rejected a bid of £4.25million for the pair from Celtic.
The offer would have allowed both players to remain at Easter Road until the end of the season.
Now representative Willie McKay fears the Scottish champions will drop their interest in the duo.
He told the Scottish Daily Mail: 'Celtic upped their previous offer today, going up to £4.25million - but Hibs knocked it back.
'Kevin and Scott are a bit upset. At a time when Celtic can go into the loan market and get full internationals through just paying their wages, I think they will just walk away from this.
'I believe it is a great offer, especially as Celtic were willing to wait until the end of the season to get them.
'That would have allowed both players to stay at Hibs and play in the CIS Cup and the Scottish Cup.'