The Blues have shipped 17 goals this term, and Keown has pointed out their inability to clear set pieces, after watching them concede three goals against Stoke City.
Keown wrote in his Daily Mail column: "It might sound funny but (manager) Jose Mourinho was scathing when he said that even the training dummies could score against Chelsea at the minute.
"The first rumblings came when they lost at Newcastle and he is clearly struggling to sharpen up his team. Saturday was the first time Mourinho had managed a team at Stoke so perhaps he underestimated them.
"They are conceding too many and they don't look like the solid unit Mourinho developed in his first spell."
Mourinho's side are currently third in the Premier League.