At the time he was saying it was where he saw himself playing to continue his career at the top, so I'd guess it's safe to say that he couldn't do it to a high enough level.
If we insist on shoe-Horning him into the side with Sigurdsson, then hasn't Sigurdsson played centre mid quite successfully for Iceland?
Personally, I'd much rather have Davies in there with his movement and forward running. Even when he's not in top form he gives us something different than any other player we have.
I'd start Davies beside Schneiderlin for sure, might give Rooney a shot when Gana starts. If it doesn't work, go with Davies full time with Klaassen backing Davies up. Rooney as a reserve for Sigurdsson or to give us a 2nd striker late.
But Sigurdsson is the future, and needs space to operate (as we saw mid-week). Need to build around that, see what we have. At least give him a solid 2-month run.