The 31-year-old is preparing for his first competitive action with the national team ahead of World Cup qualifiers against San Marino and Montenegro.
Moyes admits Osman was probably in better form when he made his debut in November's friendly against Sweden but is pleased he has been given another chance to impress.
"I am delighted for him because he has been one of the players who has carried us for a lot of the season, he really has," he told evertonfc.com.
"Yes, at times he has dipped under his best like all players will do, but so far this season he has been very good.
"It's good that Roy's continued to pick him because he was first picked at a time when he was really in top form but it's been tough for Leon because for a lot of the season he's been the one who's carried the team.
"His performances have been excellent. Whatever we've asked him to do - we've asked him to do different jobs at times - he's done it, he's come up with some important goals and he's had his best season at Everton for me.
"He's been exceptional and I'm delighted he's been given another call up by England.
"Ossie, if you were being fair, would probably be the one who, if anyone, could probably do with a week off just now because he's played all the games.
"He's been doing all the fetching and carrying for the team and he's taken a lot of the burden in terms of responsibility this season.
"We just hope he can keep that going for another couple of months."