Leedsâ€™ Italian chief Cellino says the 27-year-old Scot almost joined Cardiff during the last transfer window.
The forward netted 29 goals for the Whites last season and Cellino said: "I didnâ€™t want to sell McCormack because for me, he was the best player we had.
"I was hoping to keep a player who guaranteed us at least 15 goals and McCormack would do it.
"Iâ€™m very unhappy because McCormack decided to go for another experience.
"He tried to walk away in January to Cardiff and was already sold for ÂŁ2m but I turned it down.
"He wanted to go away for a lot of reasons he told me, his kids, his wife. He had just signed a three-year contract and he was happy with the wages and it was good wages.
"But they offered him better wages and like I told you, I was not happy to sell. I said 'OK if you want him, give me ÂŁ10m.' I said it because I was sure no one would offer it, so it was a good excuse.â€ť
Cellino was disappointed with the playerâ€™s attitude, adding: "When it came to pre-season McCormack did not come because he said he was feeling sick.
"There was a problem with his family and I was really disappointed. In his mind he was already gone.
"And then I worked a lot on a long deal and we closed McCormack for ÂŁ10,750,000.
"That is important money for the club. But, it was not in our budget to sell. I didnâ€™t like that another side from the Championship came to take our best player. If it was a side from the Premier League I wouldnâ€™t mind.â€ť
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