Mikel Arteta is expected to be sidelined for at least a fortnight, Everton head physio Mick Rathbone has confirmed.
The Spanish midfielder picked up an ankle injury in training before Sunday's Premiership clash with West Ham.
A scan on Tuesday confirmed the diagnosis of the club's medical team, and Arteta has been ruled out of this weekend's trip to Portsmouth.
Rathbone told evertonTV: 'He kicked the ground and took a hell of a chunk out of the ground. He strained the whole of his ankle.
'He actually came in the day after for a fitness test with a big swollen ankle. That swelling is now going down, and the scan has confirmed what we believed in that he has actually jarred the whole joint and not actually damaged one particular structure.
'He is making pretty good progress, and we are hoping he will be not such a long-term absentee - maybe a couple of weeks.'