The 27-year-old, who made 11 appearances for the Gunners last term after moving from Malaga for £8.5million in January, was given additional time off this summer after travelling to Brazil with Spain for the Confederations Cup.
However he is now facing a spell on the sidelines which will leave Arsenal boss Arsene Wenger short of options at left-back following the departure of Andre Santos.
Belgian defender Thomas Vermaelen has already been ruled out for up to three months with a back problem.
Wenger said: "Nacho has had an injection and it looks like he will miss the start of the season.
"Vermaelen can play there, but he is injured. At the moment we only have Kieran Gibbs who can play at left-back."