The founder of the Shirebrook-based retailer also owns the club which was just relegated from the Premier League.
Keegan, who quit the club in 2008-09 when they were last relegated had a row with Ashley over transfers and has now slammed Ashley’s mismanagement after the club's Â£80-million spending spree this season led to disaster after they were knocked down a peg by bitter rivals, Sunderland.
He said to the BBC: “It is mismanagement from the very top.
“They bought players for the future but sometimes maybe you have to buy players for the present. It’s all right having a few good young players from France but can they play in the Premier League now?
“If they can’t - don’t buy them or certainly don’t play them. A few of them have found it very tough and the confidence goes and then even good players start to look pretty poor.
“The owner has had quite a lot of years of making a lot of mistakes.
“They are going to have to go down and regroup. That’s not going to be easy.
“You have to look at Mike Ashley and say he hasn’t handled the decision-making very well or he’s given the responsibility to people and they haven’t handled it very well.
“You make mistakes in football and you get punished, especially in the Premier League now.
“The owner has had quite a lot of years of making a lot of mistakes. They are where they are and I think they will go down, but they’ll bounce back.”