The Jamaican-born youngster, who signed a lucrative new contract in December, has made 35 first-team appearances this campaign but has only started one of Liverpool's last six matches.
Sterling won admiration, and a senior England cap, for his ability to skip away from tackles and leave defenders for dead with his scorching pace but has looked jaded recently.
"It's just a very physically demanding league and what you're seeing now is more tiredness of the legs when before he could go up to people and take them on," Rodgers said on the club website.
"That zip has gone and that's down to fatigue. Was that to be expected? Yes it was."
Sterling joined Liverpool as a 15-year-old from Queens Park Rangers and made his senior debut as a substitute against Wigan Athletic in March 2012.
He nailed down a regular starting spot at the start of this season and made his England debut in a friendly against Sweden in November.
"This is a kid we're talking about so we have to take a wee step back," Rodgers added.
"What he's done since he stepped onto the pitch against Leverkusen in a friendly to Manchester City, as a 17-year-old, I dare you to look around Europe and tell me a 17-year-old who has made an impact in one of the big leagues. There aren't many.
"It is so mentally and physically draining this league. It hurts experienced professionals and this boy has just stepped up from the Academy and played football and earned a contract off that.
"We have to nurture that and at times he's got to have that mentality to keep learning. I was talking to him the other day about this, and if he didn't kick another ball this season he's had a good one."
