The French defender, 30, said: "These are tricky times for me.
"I am very unhappy at being injured all the time and I need to remain mentally strong.
"I know I ought to remain positive but it is very difficult to do so.
"I don't want to cry but when you work hard and you feel this pain it is hard to accept.
"I am strong and I will make a comeback - but when, I don't know."