NFL Media Insider Ian Rapoport reports, via a source informed of the prognosis, Mettenberger suffered an AC joint separation in his throwing shoulder.
It's the second time Mettenberger has injured the shoulder in two weeks, hardly a surprise given his statuesque pocket movement and tendency to hold the ball too long while going through his progressions.
The sixth-round draft pick will finish his rookie season with a 59.8 completion rate, 8:7 touchdown-to-interception ratio and 30.11 QBR.
The question the Titans have to ask over the next few months is whether Mettenberger showed enough potential in six starts to prevent the organization from drafting his replacement in 2015.
Although we have tremendous respect for Greg Cosell, we have been dumbstruck by the NFL Films senior producer's contention that Mettenberger has been peerless among rookie signal-callers this season.
Mettenberger certainly boasts a big arm and a willingness to squeeze the ball into tight spaces, but he is also a one-dimensional quarterback beset by a long delivery, an inability to handle pressure, slow eyes and scattershot accuracy.
Most problematic, Mettenberger couldn't move the chains until garbage time and was overly reliant on broken coverages and the occasional shot play down the field.
With early-round draft picks invested at two wide receiver spots, running back and on the offensive line, the Titans have enough young talent on that side of the ball to expect better results than they have shown this season.