"Y'all just need to wait and see," quarterback Nick Foles said.
Sproles offered only that he would be used in space, which is not breaking news. That's how he was used in San Diego and New Orleans over the last nine years. But Sproles confessed to a different excitement about entering this season, and it has to do with the possibilities of Kelly's offense.
Sproles' optimism was apparent in the spring, and it only intensified during the summer - even though he was used sparingly in the preseason. Sproles said only that Eagles fans would like what's to come. He said before the first preseason game that he did not expect to play much in August but that what the Eagles were doing in practice could become "kind of dangerous."
"It's how creative is your coach at that point, because he can do a lot of things really well," said safety Malcolm Jenkins, who was Sproles' teammate in New Orleans.
Before the first preseason game, Kelly said the Eagles would not hide Sproles. He explained that coaches already had seen enough of Sproles during his career to know he would be used as a running back, receiver, and returner. He joked that the Eagles would not put him on the offensive line.
Despite what Kelly said, it was clear that the plays called for Sproles seemed vanilla. The Eagles never used Sproles and LeSean McCoy on the field together. He was on the field only once with two tight ends. Sproles caught punts but never returned one. Even Kelly said Tuesday that there is more Sproles can do.
"You know, we're excited about him," the coach said. "I've said he's a really talented runner and you'll see him carrying the football, and he's obviously a weapon coming out of the backfield. So you'll see a lot more out of him."
The intrigue is about how much more there is to see. Sproles excelled under Norv Turner and Sean Payton - two of football's best offensive minds - and there's a sample size of eight seasons to show his many skills.
"Just use your imagination," Jenkins said. "Whatever you think you know about Darren Sproles, you probably don't. And whatever you say he can't do, he probably can."
The Eagles are committed to using Sproles in the running game, which he has said is one different way he expects to be used. He totaled more catches than carries in three of the last four seasons.
The McCoy-Sproles package also will be a wrinkle. The Eagles want to create mismatches for Sproles with linebackers, so where they align him and move him before the snap will involve the intricacies that the team has kept veiled.
Eagles defensive coordinator Bill Davis said when he coached against him, he usually needed to put a player on Sproles' side or an extra body in man coverage. Linebacker DeMeco Ryans, who has played against Sproles in each of the last three seasons, said he looks like the same player this summer as the one who caused his defenses so much angst.
"Every time I've lined up against him on another team, you've got to keep an eye on Sproles," Ryans said. "He can line up everywhere, can do anything on the field."
The Eagles have touted this quality about Sproles since they acquired him in March and immediately gave him a contract extension. On Sunday, they'll finally show why they are so excited.
"You haven't seen nothing yet," Sproles said.