Ferguson's book, which was cleared by United's lawyers, is full of attacks on Liverpool.
"When you have been a successful club like Liverpool, (with United) chasing them for so many years, you have to find ways of bringing them down," said Rodgers, who Ferguson regarded as being "a surprise" appointment to follow Dalglish, given he was only 39 when taking the role in June 2012.
"This is a club that has class; a club that has history and is fighting in the modern era to get back to where it was.
"I'm not worrying about what was said. There's been enough reaction in the past few days. I've got enough to worry about and concentrate on with my football club. He's obviously waited and felt his time to retire was the time to put a few things right. It's his right to do that.
"I understand you come to a club of this magnitude at 39 and of course it is a big ask but I've relished every minute of being here and I'll continue to do what I've always done which is give my best to protect the great values of this club."
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