That drop in form has allowed Chelsea to move within four points of second-placed City.
"The gap is very big [between United and City] and we have in our head if we win we can get very close to them," Ba said.
"We know this is not the best time for Man City at the moment and we're going to try and take advantage of that.
"It is going to be difficult to catch Manchester United because they are so many points clear from City.
"I don't see them losing that many points but we're just going to try and win the maximum possible and see where we will be at the end of the season."