The Republic of Ireland star – who was subject of Roy Keane’s outburst during the international break due to his absence through injury – limped off the pitch against Wolfsburg last night with what looked like another hamstring injury.
“His body is getting used to the demands of playing European football and international football,” said Martinez.
“It is a problem we need to look at because he has had it before.
“We need to make sure we find the right balance. We’re going to help him in that respect.
“What I’m focusing on is getting deep into the bottom of the problem and slowly allowing him to cope with the demands his role represents.”