The Cottagers face Wolves tomorrow.
On Diarra, Jol said: "If you start telling players like him that they have to prove a thing and you need to have a look at them for a couple of weeks, then it's not the trick.
"The trick is to find out if he is fit and that is the information that I had.
"We had a little look at him but he wasn't even aware of that and he's been here for two weeks. He may be involved on Sunday."