What is ailing Jeremy Maclin? (Matt Slocum/AP)

Smith’s signing gave the Eagles a low-risk, high-upside player who could provide depth to Michael Vick’s passing attack.

But the root of the decision to sign a player still recovering from microfracture knee surgery may have been aimed at filling a far more specific hole — the one left vacant by conspicuously absent wide receiver Jeremy Maclin. (At least according to fellow camp late-comer DeSean Jackson).

The third-year receiver has missed all of training camp with an undisclosed illness that Eagles officials are doing their darndest to keep secret. But word is now circulating that Tuesday could be the day Maclin’s condition is finally explained.

Maclin’s brother, Andre, told Sporting News Monday that all will be revealed soon.

“We definitely will have some news tomorrow. That’s when we find out exactly what’s going on and when (the Maclin camp) will address it and talk.

“They kind of have us on a gag order until tomorrow. ... But he’s fine, he’s fine. That much I can say.”

Eagles coach Andy Reid did not provide an update Tuesday morning but hinted news could come later in the day, saying: “There’s still some hours left in the day.”

Maclin was a force in Philadelphia’s multi-faceted offensive attack last season, catching 70 passes for 964 yards and 10 touchdowns — all career highs.

Maclin reportedly contracted mononucleosis in the spring, but the Eagles have yet to confirm the diagnosis or that Maclin’s current condition is related to that illness.