By Ryan Dunleavy | NJ Advance Media for NJ.com

As if the Giants didn't have enough tough decisions to make this offseason that could swing the 2018 season, don't forget the big one looming over 2019.

In addition to hiring a new head coach and staff of assistants, determining whether to sign Odell Beckham Jr. to a long-term extension before seeing him return to the field on a surgically repaired ankle, choosing the right veteran salary cap cuts, and scouting possibilities for the potentially franchise-changing No. 2 pick in the 2018 NFL Draft, there also is the fate of left tackle Ereck Flowers.

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Norm Hall | Getty Images

A NFL player is not eligible for an extension until after the third season of his rookie deal. With first-round picks, teams must decide whether to pick up a fifth-year contract option before the start of the fourth season.

This is nothing unusual. For the Giants, it just is more complicated than usual because it is Flowers.

Some years, like last offseason with Beckham, it's a no-brainer.

Will a new head coach and offensive line coach (his third of each) be able to get Flowers to live up his potential as the No. 9 pick in the 2015 NFL Draft? The Giants must decide by May, before that answer will be clear.

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The 6-foot-6, 329-pound Flowers is a common target of criticism from fans and ex-players alike. It seemed at times like the old regime went out of its way to lower expectations to make it feel like Flowers was meeting the bar.

With a changing of the guard all the way up to the top, Flowers is a logical candidate for the trade block if the Giants decline his fifth-year option. Or the Giants could decline it, stick with him, maybe experiment with a switch to guard and run the risk that he will play enough to deserve bigger money next offseason than the option would provide.

In that case, however, the Giants will have benefited from a much-improved player.

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John Munson | NJ Advance Media for NJ.com

Flowers, 23, has started 46 of a possible 48 regular-season games since joining the Giants and is an iron man when it comes to snap counts, but one of the two games missed was the 2017 finale.

That was general manager Dave Gettleman's first up-close look at the roster.

Anonymously sourced reports surfaced that Flowers didn't want to play in the season finale and checked out with a bad attitude. Both he and then-interim head coach Steve Spagnuolo denied the notion to NJ Advance Media — blaming a groin injury — and Flowers later said he wants to return to the Giants for a fourth season.

Pro Football Focus gave Flowers' the highest grade of his three-year career in 2017, but he still ranked as the No. 54 offensive tackle in the NFL and was rated as a poor pass-blocker and below-average run-blocker.

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Don't be too quick to write off Flowers, however.

When first-year coach Pat Shurmur said the Giants need to revamp the offensive line, he included the caveat that "some of it may be just inspiring a player on the roster to play better than he's played" and "that comes back to coaching."

How the Giants address the offensive line in free agency could be a clear indication of Flowers' future.

Here is a look at the last five offensive linemen who were picked in the first round of a draft and subsequently traded sometime before their fifth season. Trades made on draft day do not apply.

The trade returns are not what you might be expecting:

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Adam Hunger | USA TODAY Sports

OT Greg Robinson

Drafted: No. 2 pick in 2014 NFL Draft by Rams

Traded: Rams sent Robinson to the Lions in June 2017 in exchange for a 6th-round pick in 2018 NFL Draft

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Only Jadeveon Clowney was off the board when the Rams picked Robinson to be their left tackle of the future. He started 42 games over three seasons with the team but consistently graded out as one of the worst starting left tackles in the NFL, which made things extra difficult on quarterback Jared Goff as a rookie in 2016.

First-year coach Sean McVay buried Robinson on the depth chart last spring and the Rams declined Robinson's fifth-year option before trading him. He started the first six games of 2017 for the Lions but injured his ankle and was cut soon after.

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Giants free agency preview: Running back

What veterans make sense?

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Cleveland.com

C/OG Cameron Erving

Drafted: No. 19 pick in 2015 NFL Draft by Browns

Traded: Browns sent Erving to Chiefs in August 2017 in exchange for a 5th-round pick in 2018 NFL Draft

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Most of the Browns' first-round picks from 2009-15 turned out to be busts. Erving, who played in 29 games with 17 starts, was no exception. He struggled at guard and center and was beaten out in training camp when given a shot to win the starting right tackle job.

The Chiefs used Erving as a swing backup for 13 games in 2017, with four spot starts. Like the Giants with Flowers, the Chiefs have a decision to make on Erving's fifth-year option.

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Kevork Djansezian | Getty Images

OG Laken Tomlinson

Drafted: No. 28 pick in 2015 NFL Draft by Lions

Traded: Lions sent Tomlinson to 49ers in August 2017 in exchange for a 5th-round pick in 2019 NFL Draft

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When the Lions traded for Robinson, it made Tomlinson expendable. Tomlinson lost his starting job midway through his second season to rookie Graham Glasgow and only regained it after an injury left the offensive line shorthanded and forced a reshuffle.

The 49ers have been aggressive in the brief tenure general manager John Lynch, and 49ers senior personnel executive Martin Mayhew was the former Lions general manager who drafted Tomlinson. Given the price paid, his 15 starts and above-average play in 2017, Tomlinson was a steal.

Will the 49ers pick up his option?

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Mike Shula's impact on Eli Manning

A look at how other QBs have performed under Shula

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Rodger Mallison | TNS

OG Jonathan Cooper

Drafted: No. 7 pick in 2013 NFL Draft by Cardinals

Traded: Cardinals sent Cooper and a 2nd-round pick in the 2016 NFL Draft to Patriots in exchange for Chandler Jones

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Cooper's trade is different than the others because it wasn't a straight trade of an underachiever for a draft pick lower than his own draft status.

The Patriots picked up Jones' fifth-year option but traded him before his fifth year, perhaps not wanting to pay a high-priced pass usher. Jones re-signed on a $83 million contract with the Cardinals after the 2016 season and led the NFL with 17 sacks in year one of five.

Since the beginning, Cooper's career has been undone by chronic knee and feet injuries. He was cut by the Patriots without ever appearing in a game and since has played for the Browns and Cowboys. He is entering free agency off a career-best year, with 13 starts for the Cowboys.

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OT/OG Gabe Carimi

Drafted: No. 29 pick in 2011 NFL Draft by Bears

Traded: Bears sent Carimi to Buccaneers in June 2013 in exchange for a 6th-round pick in 2014 NFL Draft

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After starting 16 games at right tackle — it would have been more if not for a knee injury — in his first two seasons, Carimi skipped OTAs and voluntary mini-camp with Marc Trestman's then-first-year coaching staff in 2013 to work out away from the team. The plan was to move Carimi to guard.

There was a thought at the time that the Bears were too quick to disregard a first-round talent because he was tied to the old regime. Except that Carimi was out of the NFL after the 2014 season, spending one season with the Buccaneers (even his former Bears coach Lovie Smith cut him) and one with the Falcons.

Carimi never lived up to billing as another top offensive lineman out of the University of Wisconsin and an Outland Trophy winner as college football's best interior lineman.

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New Giants OC has longstanding relationship with top free agent offensive lineman

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Ryan Dunleavy can be reached at rdunleavy@njadvancemedia.com. Follow him on Twitter @rydunleavy.