One was senior defensive end Mark Anderson, recovering from arthroscopic surgery on his left knee.
After a star-crossed 2004, this surely wasn't the way Mike Shula wanted to start a new season.
While neither player is expected to miss much time – Barnes' mono isn't contagious, while Anderson's knee is healing nicely – Tuesday was an ugly reminder of how much injuries mean to the Alabama program.
Last season was destroyed by them.
And if they strike again, it's a quick fall to 6-5 and Christmas in Shreveport, home of the lustrous Independence Bowl, or another New Year's Eve in Nashville.
This Alabama team has talent, all across the board. Its defense is loaded, with a veteran secondary led by Roman Harper, Charlie Peprah and Anthony Madison and an excellent linebacker corps keyed by DeMeco Ryans and Freddie Roach.
Sophomore defensive end Wallace Gilberry is the only new starter – and he's coming off a freshman All-SEC season. Croyle, Kenneth Darby and a strong young group of wide receivers should provide plenty of firepower on offense if – and this is a big if – they stay healthy.
That's easier said than done, considering last season.
Two games in, the Tide was building a serious buzz following a rout of Ole Miss.
Then, halfway through a whipping of Western Carolina, Croyle tore apart his right knee – and the season fell apart.
And Darby shredded his groin at LSU.
By the Music City Bowl, a skeleton crew – Pennington, tailback Aaron Johns and a gimpy Le'Ron McClain – stood behind a patchwork offensive line, and the results weren't pretty.
The offense was a shell of itself, which made 6-6 and a minor bowl berth look like a major accomplishment.
A year later, the hurting are mostly healed and the expectations accordingly higher. Croyle has looked like his old self through two practices, with no visible signs of pain.
Darby has cut and juked just like he did during his breakout sophomore season, a highly positive sign considering how a groin injury can handcuff even the most flexible player.
The third member of the surgery triumvirate – Castille – is moving slightly slower than his teammates, but expects to be full-speed within the next two weeks.
If all three come back completely healthy, Alabama could be one of the SEC and America's surprise teams.
The defense should be excellent. Add Darby, Croyle and Castille to a maturing offense with good young wide receivers, and points could pile up, providing a rebuilt offensive line holds its ground.
Staying healthy, however, will be absolutely crucial. 77 scholarship players took the field Tuesday – eight below the 85-player limit allowed by the NCAA. Shula's program is recovering from the serious scholarship reductions imposed by NCAA probation, but it will be at least another year before Alabama reaches 85 scholarships.
If Croyle gets hurt again, freshman John Parker Wilson will likely be thrown in the fire.
All three are talented players who should have great careers, but suggesting any of them are ready for the spotlight of starting is foolish at best.
So is suggesting Alabama will skate through 2005 injury-free. Football is a violent game, and nicks and bruises simply come with the territory.
Somewhere along the line, a key player will come up lame – for a game or for the year – and his teammates will be forced to fill the void.
That's not a guess. It's fact.
What no one knows is how many key injuries will pile up this fall. One won't hurt too badly (unless it's Croyle), but two or three could be absolutely crippling, turning a breakout season into a bust.
If a bad case of mono is the worst thing Shula has to worry about this fall, it'll be a special season, indeed.
Right now, though, excuse Tide coaches and fans if they cross a few fingers and hold their breath.
It's been that kind of year in Tuscaloosa.