The injury to Laporte was a significant event for City, as it robbed them of their best centre-back for much of the season.
And Dixon believes it is the reason why they are nine points behind Liverpool.
He told reporters: "I'm trying to put it down to one thing, I would probably say Laporte getting injured for me is the biggest factor.
"I think he is a brilliant defender, I think he holds down that left-hand side of the defence, whoever is playing at left-back he can kind of control that side of the pitch and obviously his centre-half on the inside.
"You can put a body in there and I think that's been a problem at centre-back as is well-documented, with Fernandinho going in there who's a brilliant footballer but he's not got that sixth sense of somebody just nicking in-behind him off his shoulder.
"The amount of times you go 'they're in position' but somehow someone gets in, the little ones around the corner are difficult to deal with, especially around the box."