Jewell said: "Nathan was really under the weather last week so he's had a couple blood tests.
"Maybe the long season has caught up with Nathan, because it has proved a tough and demanding campaign for him.
"He has never worked as hard in his football life before and never played as many games, so I thought I would give the lad a rest last weekend, although he did have to come on for Neil Roberts in the second half.
"I'm not feeling sorry for him, because playing football for a living is a fantastic career for a young man, but he has had a tremendous workload to deal with this season."
Ellington's 19-goal return has fired champions-elect Wigan to the verge of Division One, but Jewell believes there is plenty more to come from the quicksilver 21-year-old.
Jewell added: "Nathan has improved tremendously as a player since he arrived with us from Bristol Rovers a year ago, but he still has a lot to learn as well.
"He has got better in all areas of his game, and I'm convinced that there is still a lot of untapped potential there.
"If he continues to show that sort of improvement, development and desire then he can be an even better player for Wigan."
Defeats for Wigan's nearest rivals Crewe and Cardiff, left Wigan with a huge 14-point cushion at the summit with just 10 games left on the fixture card.
Jewell said: "It is probably a measure of how far we've come over the past year that the boys were disappointed with a 1-1 draw at Peterborough.
"We didn't play to our normal excellent standard there, but nobody asks more from my players than me, and maybe I'm a little bit of a harsh judge on occasions."
Wigan's Reserves won 2-0 at Stoke yesterday afternoon.
Article from the Wigan Evening Post.