The Pittsburgh Steelers' biggest free agent signing of 2016 might end up being their biggest bust.

When the Steelers signed Ladarius Green to a four-year, $20 million contract in March, the hope was that Green would take over the No. 1 tight end spot from Heath Miller, who decided to retire after the 2015 season.

Unfortunately for the Steelers, the transition from Miller to Green isn't going so well, and that's mainly because Green hasn't been on the field yet.

Even worse for the Steelers?

There's a chance Green might not ever get on the field.

According to NFL.com, Green has been dealing with constant headaches that have kept him sidelined for the past five months. Although it's not clear when Green's headaches started, he did miss one game due to a concussion last season, and that came after he suffered two concussions during an 11-day period in September while he was with the Chargers.

According to Pro Football Talk, Green's headaches have become so severe that the tight end is now contemplating retirement.

When Green originally signed with the Steelers, the team knew that he was coming off January ankle surgery that would likely keep him out for a few weeks, which is what happened. Green missed every single one of the Steelers' offseason workouts and OTAs between April and June.

The Steelers assumed Green would be healthy enough for training camp, but that didn't happen because of the headaches that he's been battling.

If Green ends up missing any game time, which is looking likely at this point, the Steelers are going to want to know when his headaches started.

Basically, the headaches could end up causing a financial headache for Green, because he could be out some serious money due to his head injury. According to the Pittsburgh Post-Gazette, Green didn't tell the Steelers about his headaches before he signed with them in March. If that's the case, the Steelers could try and recoup some of the money that they've given to the former Chargers tight end already.

If Green withheld injury information, then the Steelers could potentially get the back the $4.75 million signing bonus they gave Green. On the other hand, if the Steelers can't prove anything, there's a chance that Green could keep the entire signing bonus, even if he never plays a down in Pittsburgh.

Even Steelers coach Mike Tomlin isn't sure what's going to happen with Green.

"He's progressing, but we really thought it would be touch-and-go up to this point," Tomlin told NFL.com.

If you're thinking about drafting Green in your fantasy league because the Steelers have such an explosive offense, don't do it!

As our fantasy guy Heath Cummings notes, you should only take Green if you're desperate in the late rounds of your draft.