It's tough to imagine Joe Staley playing for another NFL team. Luckily for fans, they don't have to. The veteran tackle was preparing to enter the final year of his deal when the San Francisco 49ers offered up a two-year extension.

The new contract means that Staley is signed through the 2021 season and is likely to finish his impressive NFL career with the team that drafted him in 2007.

Staley received Pro Football Focus' sixth-highest overall grade among tackles last season and the eighth-highest overall grade among all offensive linemen. He has graded as one of the top six tackles during all but one of the past five seasons and was the highest-graded in 2017.

Below is a breakdown of Staley's Pro Football Focus grades for each of the past five seasons with his rank among NFL tackles listed within parentheses.

Year Overall Pass Block Run Block
2018 82.2 (6) 83.8 (12) 75.4 (8)
2017 89.6 (1) 85.2 (5) 85.2 (2)
2016 81.1 (17) 77.0 (34) 76.8 (16)
2015 90.5 (4) 85.4 (9) 87.7 (5)
2014 89.1 (4) 83.2 (15) 90.4 (1)

While stats and analytics are nice to have, nothing is more telling than watching a player's on-field performance. That's exactly what general manager John Lynch and head coach Kyle Shanahan did after last season. It's also what convinced them that Staley had to be locked in for more than one more season.

"We went back and watched it (Staley's film) in the offseason, and it was even more impressive than we thought, so he earned it, first and foremost, by that," Lynch said last week via NBC Sports Bay Area.

The lineup on offense has seen a dramatic change since Lynch and Shanahan took over. Shanahan noted during the team's State of the Franchise event that the roster turnover has been so drastic that Staley is the only remaining starter from the previous regime.

Offensive line continuity is one of the storylines headed into the 2019 season. Staley knows the unit has room for improvement, but the line will improve with the return of its starters.

"The guys are working really, really hard right now to build on what we did last year," Staley said last week during the State of the Franchise event. "Last year was not perfect for us, but we have a lot to improve on. We're doing that right now. We're doing the little things right now in practice that we can do."

Each starter from last season is expected to have the same role this year, and each starter is signed through at least the 2021 season. Tackle Mike McGlinchey and guards Laken Tomlinson and Mike Person are signed through 2021. McGlinchey, however, can be secured through the 2022 season thanks to the 49ers' fifth-year option. Center Weston Richburg is signed through 2022 as well.

"That is very rare in the NFL, especially in this day and age with free agency, and guys leaving, coming, and going, and everything, to keep the same group of five guys year after year," Staley said. "Hopefully we can do it not just this year but years forward."

"It's extremely important to have the five guys back in the same positions as we were last year," McGlinchey added. "It builds a lot of chemistry moving forward."

McGlinchey will likely take over the left tackle spot once Staley calls it a career. For now, he doesn't have to be worried about being separated from his friend and mentor. As for the other tackle spot, there is no definitive answer who will eventually anchor it.

"If [Staley's] not here, what's it going to look like? And we didn't like that," Lynch said. "Not that there are not candidates on our roster. We feel better than ever about our depth, but Joe is a big part of this team in so many ways. It made too much sense (to extend his contract)."

No one wants to close the door on Staley potentially playing beyond the 2021 season, but deep down, the veteran tackle knows this was probably his last time signing an NFL contract.

"I was telling some media people yesterday (last week), I didn't want to completely close the door, but that's going to be the last contract I sign, probably, in the NFL, if I were to guess," Staley said last week during a KNBR interview. "I think 15 years is going to be a long time. I'll be in the NFL for a long career, so I feel like this is going to be the last one."