HITC Sports understands that Boro are expected to make new bid after pulling out of Jordan Rhodes deal.
Boro had pulled back from a deal for McCormack on Friday and pushed ahead with a move for Rhodes, who was on Teesside for talks on Saturday morning.
However, the Championship club stated on Sunday that they could not agree personal terms but HITC Sport has been told by Rhodes' camp that this is not the case.
HITC Sport understands Middlesbrough chairman Steve Gibson personally pulled the plug on the deal and has now given the green-light to once again try to prise McCormack away from Fulham.
McCormack has been determined to leave the club and put in a transfer request on Thursday - but Fulham want him to stay and are willing to offer him a new contract.
The 29-year-old has scored 17 goals in 31 matches so far this season and he would be a fine addition to Boro's forward-lie if they can get a deal done by close of business on Monday.