Everton boss David Moyes has confirmed Mikel Arteta has suffered an injury setback.
The midfielder, who sustained a cruciate knee ligament injury in February, has had to undergo a procedure to remove an infection from the same knee and is now recovering.
Moyes told evertonfc.com: "Mikel has needed to have a 'wash out' on his knee after doctors found an infection.
"It is a setback for him. However we can't say how long it has put him back."