Stoke City came close to signing Ba in January 2011 but a deal was not finalised after he failed a medical.
"My left knee? There was absolutely no problem on that level with Chelsea," the striker said in L'Equipe.
"I don't like to talk about that, but just have a look at the number of matches I have played since I have been in England (65 in the Premier League). The answer should be enough to satisfy everyone."