The New England Patriots have a mysterious situation with second-round NFL Draft pick and edge rusher Gabe Jacas ahead of training camp.

Jacas, who remains unsigned and is the only second-round pick who hasn’t inked his rookie deal, was not around for mandatory minicamp last week.

Head coach Mike Vrabel confirmed that Jacas wasn’t with the team for minicamp and that the rookie had a procedure, although he didn’t go into specifics on what the procedure was.

Now, ESPN’s Mike Reiss is reporting that the procedure was a “clean-up” on Jacas’ knee.

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The mystery there is it isn’t clear what happened to necessitate Jacas’ procedure, and Reiss reports the Patriots don’t know, either.

“But a source familiar with Jacas’ recovery said he underwent a knee procedure that was described as a ‘clean-up,'” Reiss reported. “It is not known whether something happened after Jacas’ physical exam and subsequent recheck at the combine, or when the Patriots had him in for a predraft visit the week of April 20, and that information wasn’t disclosed to the team.”

Why Gabe Jacas isn’t with Patriots

Reiss adds that Jacas hasn’t been with the team since May, and part of the reason for that is the Patriots not being willing to give him a “participation agreement.”

“Jacas hasn’t been with the Patriots since May, according to a source. His absence is tied, in part, to not being given a standard ‘participation agreement’ from the Patriots, according to a source,” Reiss reported. “Most draft picks receive such an agreement, which states that if they were to sustain an injury prior to signing their first NFL contract, the team would still be obligated to sign him to a contract based on the slot he was drafted.”

One potential reason for the hold up with Jacas’ contract is the Patriots could be looking for “a level of financial protection in the contract based on the medical procedure,” one NFL executive told Reiss.

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The expectation, according to Reiss, is that Jacas’ procedure won’t cause a long-term issue and the hope is he’ll physically be ready to roll for training camp.

However, it remains to be seen if this standoff between Jacas and the Patriots will extend beyond the start of training camp, which begins on July 25.

Why Gabe Jacas’ offseason absence is bad news

A rookie like Gabe Jacas can ill-afford to miss practice time in their first season.

That’s because it’s hard enough to get acclimated to the NFL with a full allotment of practice time. Not having any so far will almost certainly stunt Jacas’ growth, and that will only get worse the more time he misses.

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Adding to that, Jacas isn’t likely to have much of a role, if any at all, to begin the season — and that’s especially true on a team run by Vrabel, who is not the kind of coach to hand a rookie anything.

That is bad news for the Patriots, who could use a jolt in the pass-rush from Jacas after the team finished tied for the seventh-fewest sacks in the NFL last season.