ST. LOUIS -- As Chris Carpenter and Adam Wainwright continue their respective marches back to the Cardinals' active roster, timing becomes a tricky issue for the club's front office.

No one wants to rush Carpenter, who is returning from Tommy John reconstructive elbow surgery, or Wainwright, who sustained a finger injury on his right hand. But with the non-waiver trade deadline just 11 days away, the Cardinals need to figure out just how much they expect to get from their recuperating aces.

"I'm definitely walking a fine line now, because you don't have a whole lot of time after [July] 31 to get an easy deal done because of the waivers," Cardinals general manager John Mozeliak said. "But I do think we're going to have a pretty good indication before we get to the 31st where those guys really stand. It's a tight window, I give you that. But it's one where I think if we're trying to stick to the plan we have maintained throughout, we have to [take] that approach."

Carpenter's recovery takes a major step forward on Sunday when he begins a Minor League rehabilitation assignment at Double-A Springfield. Wainwright hopes to throw off a mound in the coming week. Mozeliak said it's likely that Carpenter will return to the rotation before Wainwright, but acknowledged that such estimates remain fuzzy.

In the meantime, the Cardinals would also love to add a relief pitcher, preferably a left-hander, and perhaps an offensive upgrade. But Mozeliak said that even moves that might be considered minor are hard to get done right now.

That is, even to add something like a left-handed relief specialist or a bat off the bench could be prohibitively expensive in terms of the players the club would have to give up.

"It's hard to guess, hard to say," Mozeliak said. "Right now, the delineation of who's in and out is getting more clear, but the cost of doing business right now seems extraordinarily high."