Liverpool manager Brendan Rodgers feels the demands of the season have taken their toll on teenage star Raheem Sterling.
The 18-year-old winger has made a huge impact since being handed his full Barclays Premier League debut by Rodgers last August.
His progress earned him an England cap against Sweden last November and a new five-year contract but he has not completed a full 90 minutes since December.
Rodgers believes fatigue is a factor.
Rodgers told reporters: "It is so mentally and physically draining, this league.
"It hurts experienced professionals and this boy has stepped up from the academy, played football and earned a contract off that.
"We have to nurture that and, at times, he has to have the mentality to keep learning.
"If he didn't kick another ball this season, he's had a good one.
"But what you are seeing now is more tiredness of the legs when before he could go up to people and take them on.
"That zip has gone and it's down to fatigue. Was that to be expected? Yes it was."