The Eagles will be without Mike Patterson for at least a month, and likely longer, with the defensive tackle still recovering from offseason brain surgery.  Patterson started at least 14 games for Philadelphia in each of the last six years.

“We’re talking about this preseason as a month, and then we’ll probably re-evaluate from there, but it could be a couple months, or more,” said Rick Burkholder, the Eagles head athletic trainer.

Patterson had a seizure during training camp last year and doctors discovered an arteriovenous malformation, or a tangled mass of blood vessels, in his brain. Patterson returned in just 10 days to begin conditioning and started 15 games for the Eagles before undergoing surgery in late January.

The Eagles expected to have the 28-year-old back for the start of training camp, but part of his skull, which was removed and replaced during the surgery, has not fully healed. Patterson had an x-ray and CT scan examined by Dr. Robert Spetzler, a neurosurgeon in Phoenix, Ariz., who made the decision to hold him out longer.

“[The physician] wasn’t totally happy with it,” Burkholder said. “He liked the healing, but he’s concerned about some very small situations that he could get into in football.”

Burkholder said the Eagles and Patterson are optimistic he’ll play again, but did not offer a firm timeline on his return.  Meanwhile, head coach Andy Reid says the Eagles prepared for this possibility even though they expected Patterson back by now.

“We took precautionary measures and we made sure at that position that we didn’t come up short,” Reid said. “We have players that were with us last year that contributed and we added a couple new players in there.”

The Eagles drafted Fletcher Cox in the first round, moving up from 15th to 12th to grab the defensive tackle from Mississippi State.  Cox was expected to contribute as part of the four man rotation in his rookie year, but now his role may be magnified.

“First round draft picks you expect a lot out of,” Reid said. “We’ve had success with that position and guys getting in and playing early, so I would anticipate when he gets in there, he’ll be working with the ones and doing that.”

Cullen Jenkins is the Eagles top returning defensive tackle, with 16 starts and 5.5 sacks last year.  In addition to Jenkins and Cox, the Eagles will rely on Antonio Dixon and Derek Landri.

Dixon was sidelined with a torn triceps in Week Four last year, but started 10 games and provided a strong presence against the run in the middle in 2010.

Landri played in 12 games last year, notching two sacks and 21 total tackles. Two years ago, the 28-year-old started 16 games in Carolina and finished with three sacks and 43 tackles.

“I consider the four guys starters,” Reid said. “You put four guys in the mix and that’s what you’d like to come out with and then those four, you’re going to play them. Try to get them equal opportunity.”

Patterson will begin the preseason on the Reserve Non Football Injury list.  The Eagles can restore Patterson to the active roster at any time between now and the end of the preseason.

At that point, if Patterson remains on the N-F/I, he’ll be out until at least Week Six.  Players on the N-F/I can practice for up to 21 days beginning anytime between their team’s sixth and ninth game, after which point they must either be activated or their season comes to an end.

In the mean time Patterson, who reported to camp yesterday, can perform conditioning work and take part in meetings.

Injury Report

Safety Colt Anderson starts the season on the Physically Unable to Perform (PUP) list, which is subject to the same rules as the N-F/I. Anderson, known for his special teams prowess, tore his ACL in December.

Left tackle Jason Peters starts on the N-F/I list, after rupturing his Achilles tendon twice in the offseason.  Reid admitted that it’s unlikely Peters will return at all this year, but there’s no reason for the Birds not to keep him on the N-F/I until Week Nine, thus preserving the option of his return just in case Peters makes a stunningly quick recovery.

Several Eagles dealt with injuries during the offseason or mini camp, but are ready to go for training camp, including tight end Brent Celek (hip surgery), offensive lineman Jason Kelce (foot sprain), linebacker Moise Fokou (ankle surgery), linebacker Jamar Chaney (neck surgery), linebacker Keenan Clayton (sports hernia), linebacker Mychal Kendricks (knee inflammation) and defensive end Vinny Curry (high ankle sprain).

Roster Moves

The Eagles traded cornerback D.J. Johnson to the Colts in exchange for defensive tackle Ollie Ogbu. After three years as a starter at Penn State, Ogbu spent last season on the Colts practice squad.

The Eagles also signed wide receiver Anthony "Tiger" Jones, who played for the Philadelphia Soul in the Arena Football League last year, and Kee-ayre Griffin, a wide receiver from Temple.

Ryan Messick covers the Eagles for 97.3 ESPN FM.  Follow him on Twitter.