The Scotland international has now been the subject of three bids from Boro as they look to try and strike a deal with their Yorkshire rivals.
McCormack, who scored in the weekend draw with Sheffield Wednesday, admits he is happy with the club and remains committed, but concedes that he could leave if Leeds accept an offer.
Boro themselves have looked light on firepower throughout the early exchanges of the season and manager Tony Mowbray is desperate to add to his options, and could bring in two new front-men before the transfer deadline at the start of September.
Despite his lack of options, Mowbray has again admitted that Dutch forward Marvin Emnes, who came off the bench to score a last-gasp equaliser against Blackpool on Saturday, could yet leave the club.
"Let's see what the next few weeks brings with Marvin," said Mowbray.
"If he stays he will definitely help us. He is the type of player we like - comfortable with the ball at his feet.
"He scored 18 goals two seasons ago, and I want to help him. I like Marvin. I always have done. When I arrived he was on loan at Swansea and I brought him back.
"His career here has been high then low, high then low.
"He hit the ground running when he came back from Swansea and scored goals. Last season he fell away but we will keep working with him."