Running back Ka'Deem Carey was the rock of Arizona's offense through head coach Rich Rodriguez's first two seasons in Tucson, rushing for more than 3,800 yards in back-to-back eight-win seasons.
His decision to forgo his final year of eligibility and pursue an NFL career leaves Rodriguez with a dilemma.
Rodriguez's offense has featured plenty of impressive running backs, from Avon Cobourne and Steve Slaton at West Virginia to Carey at Arizona. But it's hardly as simple as plug-and-play a running back into the system and watch him go for more than 1,500 yards.
A hallmark of Rodriguez's version of the zone-read spread offense is its variation by personnel.
It's had standout running backs, of which Carey may be the most recognizable. But it's also had dual-threat quarterbacks Denard Robinson, Pat White and Rasheed Marshall carry for big yards.
In Rodriguez's first year at Arizona in 2012, the team even featured a potent passing attack behind quarterback Matt Scott. With Carey leaving, expect the offense to take on a different look in 2014 than it had last year.
Carey was a throwback operating within Rodriguez's modern offense, rushing dozens of times per game with a grinding style that turned minimal gains into big ones. He took on a heavier workload in 2013 than 2012 when he led the nation in rushing, carrying 349 times in 12 games as opposed to 303 in 13 outings the year before.
At 5'10", 207 pounds, Carey combined power with speed, the necessary combination for his many highlight-reel runs through would-be tacklers. His strength also allowed him to handle that especially high workload.
"He's 10 or 15 pounds bigger than last year," Rodriguez said of Carey on the Nov. 26 Pac-12 coaches teleconference call, just days after the running back's signature performance: a 48-carry, four-touchdown showing in Arizona's upset of Oregon.
"He's extremely strong and great in the weight room," Rodriguez added. "He runs so hard and has some kind of quirky moves, a lot of [tacklers] don't get clean shots on him."
Of the candidates to fill in as Arizona's feature back, redshirt freshman Pierre Cormier and junior Jared Baker are less than 190 pounds—and Baker is out for the offseason, nursing a torn ACL. Redshirt freshman Zach Green is more of a power back at 5'10", 220 pounds.
Nick Wilson, a 4-star prospect according to 247Sports.com, is an intriguing possibility. However, as Arizona Daily Star beat writer Daniel Berk points out, Wilson won't join the team until the summer.
Replacing Carey with one player isn't necessarily realistic. Even trying to run as frequently as the Wildcats did with Carey in 2013 might not be the answer.
The good news for Rodriguez is he has options to reconfigure the offense without Carey.
The Wildcats' 42-19 rout of Boston College in the AdvoCare V100 Bowl last month offered a sampling of how the offense may look in 2014. Carey rushed for 169 yards, his 16th straight game over the century mark, and scored two touchdowns.
However, the passing game shined too, setting the tone for the Wildcats' lopsided win.
Quarterback B.J. Denker threw for 275 yards and two touchdowns, connecting primarily with freshmen Nate Phillips and Trey Griffey.
Denker relied heavily on first-year players throughout the campaign.
Phillips, a true freshman, earned a nod as a Football Writers Association of America Freshman All-American for his 51 receptions, 696 yards and seven touchdowns.
Fellow speedster Samajie Grant, a true freshman, was also an integral part of the passing attack, finishing second behind Phillips with 47 receptions. Meanwhile, redshirt freshman Griffey came along at season's end.
Arizona also returns Garic Wharton, and big target David Richards has an offseason to recuperate from the injuries that plagued his sophomore campaign.
But the key piece to the Wildcats establishing a dangerous aerial attack is the reintegration of 2012 star Austin Hill into the lineup.
Hill had 1,364 yards and 11 touchdowns in 2012 but missed this past season with a torn ACL.
Rodriguez proved in his first season at Arizona he won't shy from the pass.
Scott threw 499 passes in 2012, 118 more than Denker attempted this season.
Arizona's next quarterback—Texas transfer Connor Brewer and Rivals.com Top 100 2013 prospect Anu Solomon are two of the notable contenders to replace Denker—is going to have one of the deepest groups of wide receivers in the Pac-12 at his disposal.
But he won't have Carey.
Quotes obtained firsthand unless otherwise noted.