If one is a coincidence, two is a concern and three is a trend, then job of linebacker in the NFL is trending in a bad direction with a rash of injuries that complicates deciding who are the best in the business.

In this chapter of a series by The Sports Xchange, linebackers were evaluated by reporters covering each team, but injuries are a complicating factor in analyzing what otherwise would have been the top units in the league.

Some of the best, if not the best, linebackers are spending more time in rehabilitation and/or on injured reserve than playing the game.

On Tuesday, that M.A.S.H. unit of sidelined linebackers added the name of Buffalo's brilliant young Kiko Alonso, while in Dallas star middle linebacker Sean Lee was placed on injured reserve and, in desperation, the Cowboys traded for controversial former first-round pick Rolando McClain. The Falcons also lost Sean Weatherspoon (Achilles) to an offseason injury.

Other great linebackers sidelined too often include Houston's Brian Cushing, who is making a second comeback in three seasons, and, most dramatically, San Francisco's NaVorro Bowman, possibly the most dynamic inside linebacker in the NFL last season.

And, yes, that is claiming he was better than teammate Patrick Willis, who is still among the best even if he is a step slower, and Carolina's consistent Luke Kuechly, whose text-book play is the key to a defense built around his ample abilities.

Bowman's season came to a sudden and shocking end in the NFC Championship Game when he blew out his knee while making a remarkable goal line play, although the officials fouled up the fact that he actually caused and recovered a fumble.

It was of little solace that because of that play the league made a subsequent rule change that would have allowed a review that certainly would have changed the call on the field. It was a horrid end to a season in which Bowman was arguably the best big-play -- as in game-changing -- inside linebacker in the NFL.

Bills general manager Doug Whaley confirmed Wednesday morning that Alonso, who was already rehabbing a back injury, sustained a significant knee injury while working out on his own in Oregon.

"We have updated information regarding Kiko Alonso from yesterday. Unfortunately, he suffered a torn ACL in his left knee and will most likely miss the 2014 season," Whaley said in a statement. "He will be scheduled for surgery in the near future and begin a rehabilitation program at the appropriate time. We feel badly for Kiko because he has worked very hard this offseason in preparation for the upcoming season, but we look forward to his return with his style of play that made him one of the league's outstanding rookies in 2013."

Alonso was a second-round draft pick (46th overall) whose great rookie season included 159 tackles, four interceptions, one forced fumble, two sacks and was honored as NFL Defensive Rookie of the Month last September.

As for McClain, the Ravens already tried and failed to get him to show the ability that enticed the Raiders into spending their No. 8 overall pick for him in the 2010 draft. He opted to announce his retirement, from which he is now emerging for yet another try in Dallas.

McClain played three seasons in the NFL, leading the Raiders in tackles in 2011. After several off-the-field incidents, he was cut by the Raiders in April 2013. He signed a one-year contract with the Ravens, then he claimed to have retired from football in May 2013.

McClain has not played since 2012, but he is only 24 years old, and has experience playing middle linebacker in a 4-3 scheme, the position the Cowboys need filled after Lee's season-ending injury during offseason workouts in May.

In the midst of all this mayhem, here is analysis by Sports Xchange reporters covering each NFL team:

ARIZONA CARDINALS

--LINEBACKERS: Starters - WLB John Abraham, ILB Kevin Minter, ILB Larry Foote, SLB Matt Shaughnessy. Backups - OLB Sam Acho, OLB/ILB Lorenzo Alexander, OLB Alex Okafor, OLB Marcus Benard, ILB Kenny Demens, ILB Ernie Sims, ILB Glen Carson.

Karlos Dansby and Daryl Washington were among the better tandems in the NFL and both are gone, Dansby to free agency and Washington to a minimum one-year suspension. The position is the biggest weakness on the team. Minter, a second-round pick a year ago, played one defensive snap. Now, he's making the calls. Foote is 33. Neither player is known for his pass defense. The outside positions are in much better shape. Shaughnessy is steady and tough, while Abraham (11.5 sacks) proved he has plenty left at age 35. Acho and Alexander started the first three games before going down with injuries. Acho and Okafor, who both missed most of last season with injuries, are healthy. If they stay that way, the team has great depth at outside linebacker.

ATLANTA FALCONS

--LINEBACKERS: Starters -- SLB Prince Shembo, MLB Paul Worrilow, WLB Joplo Bartu. Backups - OLB Marquis Spruill, OLB Walker May, OLB Jacques Smith, OLB Tyler Starr, ILB Yawin Smallwood, ILB Brenden Daly.

The unit was decimated by the loss of Sean Weatherspoon, who will be out for the season with a torn Achilles tendon. Shembo will be placed on the fast track to the starting lineup. Worrilow and Bartu ended last season as starters. Both were productive and flashed some ability. The Falcons are looking for linebackers, who can rush off the edge and drop in coverage.

BALTIMORE RAVENS

--LINEBACKERS: Starters -- OLB Terrell Suggs, OLB Courtney Upshaw, ILB Daryl Smith, ILB C.J. Mosley. Backups -- OLB Elvis Dumervil, ILB Arthur Brown, ILB Josh Bynes, OLB Nick DiMarco, ILB Albert McClellan, ILB Zach Orr, OLB Pernell McPhee, OLB John Simon, ILB Austin Spitler, OLB D.J. Roberts.

Although he's been in the NFL for a decade, Smith is one of the most underrated all-around defenders in the NFL. Smith remains fast in pursuit, sharp in pass coverage and is a good blitzer, contributing 123 tackles, three interceptions and five sacks last year as he proved he has plenty of good football left in him. Mosley is the front-runner to start next to Smith at inside linebacker. Suggs made the Pro Bowl for the sixth time, but the Ravens want to see him become more productive for the entire season after watching him wear down last year with just two sacks in the final nine games. In a situational pass-rusher role, Dumervil delivered 9.5 sacks before an ankle injury slowed him down. Upshaw unselfishly stuffs blockers and sets the edge at strong-side outside linebacker.

BUFFALO BILLS