Foster, 29, is the all-time leader in rushing yards and touchdowns for the Texans by a significant margin after first joining the team in 2009 as an undrafted free agent who spent most of his rookie year on the practice squad. With 6,472 career rushing yards and 54 rushing touchdowns, Foster is top 75 all-time in both categories, but the $6.5 million owed to him in 2016 could loom large for a 30-year-old running back coming off yet another major injury.
For now, the Texans are lamenting the loss of one of the few offensive leaders on a team that is 2-5.
"I feel terrible for him," O'Brien said on Sunday. "I think he's done a lot in the two years that I've been here. He's done a lot for us and I feel bad for him. That's all I can tell you. I hate that part of the game, there's nothing you can do about it but I feel bad for the guy."
Stepping in for Foster will be Alfred Blue, a sixth-round pick in 2014, who started for the Texans earlier in the season.
Injuries have been a consistent problem for Foster
One of the many factors that contributed to Foster going undrafted in 2009 was a pulled hamstring that prevented him from working out at the NFL Combine. After sitting for most of his rookie season and breaking out in 2010, Foster struggled with nagging hamstring problems for parts of 2011.
But it wasn't until 2013 that injuries started to become a serious issue for Foster. He played just eight games while dealing with back problems that eventually required surgery to repair. While he came back to earn a Pro Bowl nod in 2014, he dealt with hamstring and groin problems throughout the season. A torn groin in training camp in 2015 required surgery to repair.
The injuries cost Foster a lot of games over the last few seasons, but none were as serious as the Achilles tear he now has the tall task of coming back from.
Changes are necessary for the Texans
The Texans are 2-5, switching quarterbacks on an almost weekly basis and struggling to stop opposing offenses. The addition of young talent is a must for the team and keeping Foster for $6.5 million in 2016 might not be considered worth it for the team.
Prior to his injury, Foster was averaging just 2.6 yards per carry and 40.8 rushing yards per game. While he added 227 receiving yards, Blue, Chris Polk and Jonathan Grimes are all averaging at least 3.5 yards per carry.
Even if the Texans choose not to upgrade the running back position in the offseason, the team could decide that its three running backs (all 26 and under) are the better options for the future, similar to a year ago when the Texans decided to move on from wide receiver Andre Johnson after 12 seasons.
Success after 30 is rare for running backs
Foster will turn 30 just before the beginning of the 2016 season and that's a tough age to continue to find success, even when healthy. Only four players have managed to finish a season with more than 1,500 rushing yards at the age of 30 or older. Tiki Barber and Walter Payton each did it twice, while Corey Dillon and Curtis Martin both managed more than 1,600 yards and 12 total touchdowns in a season after turning 30.
With a torn Achilles now in his history, it's unfair to ever expect Foster to return to the form of earlier in his career when he recorded four seasons of 1,200 yards or more. Even becoming a feature back again would be an accomplishment for Foster, whose likely best bet is to find a place where he can be a complementary back. That's something that is rarely worth $6.5 million.