The Detroit Lions have a primary issue and a potential opportunity regarding quarterbacks, and neither involves drafting one.

Negotiating a contract extension for starter Matthew Stafford is an offseason priority for general manager Bob Quinn.

With no need to draft a quarterback, listening to trade offers is a possibility. The Lions are at No. 21 in the first round, and three teams below them could look to move up – the Texans at 25, Saints at 32 and Browns at 33.

The Lions are set with Stafford the starter and Jake Rudock his backup. Stafford is on the last year of his contract. Timing seems to be the only question in getting a new deal.

"These things don't usually happen in April or May," Quinn said at the Combine. "That's not a realistic timeline for an extension for a quarterback."

The top four prospects in some order are Deshaun Watson of Clemson, Mitchell Trubisky of North Carolina, DeShone Kizer of Notre Dame and Patrick Mahomes II of Texas Tech.

Lions QB draft priority: As low as it gets.

Free-agent impact: Zilch.

Trade options: This is pure speculation, and any move by the Lions involving a quarterback definitely would be done with teams who have different reasons for moving up. The Texans and Browns are looking for new starters. The Saints, with a first-round pick at No. 11, could look to draft and groom a successor to Drew Brees.

Lions QB Draft Breakdown: How QB draft helps the Lions, depth chart, stats, capsule highlights of the top 5 QBs and other notable prospects, and the Spotlight Player.

What helps the Lions: Every QB drafted before the Lions make their first pick at No. 21 leaves a player on the board from a position that could help the Lions.

Depth chart: The top two are set -- Stafford the starter, Rudock the backup. Dan Orlovsky, the backup the last three years, will not be back.

Iron man: Stafford needs one more start to hit the 100-game mark for consecutive starts. He began his streak on opening day of 2011. He has 96 straight starts in the regular season and three in the playoffs.

Only three current quarterbacks have an active streak longer than Stafford's, including playoffs. They are Eli Manning of the Giants (199-12, 211); Philip Rivers of the Chargers (176-9-185) and Matt Ryan of the Falcons (115-6, 121).

Top 5 QB prospects:

1. Mitchell Trubisky, North Carolina: A one-year starter whose ability and potential have moved him ahead of more experienced quarterbacks. Trubisky was a backup before 2016 and decided to come out early, based on his 2016 season performance.

Stats line: 13 games, 68 percent completion rate, 3,748 yards, 30 TDs, 6 interceptions.

Measuring in at 6-2 at the Combine met the height requirement. Now he can move on to bigger things.

2. Deshaun Watson, Clemson: A proven winner in college, he led Clemson to the NCAA championship game against Alabama the last two years. The 2016 team won the championship.

Stats line: Threw for 10,163 yards and 90 TDs in three years, with 4,593 yards and 41 TDs in 2016.

3. DeShone Kizer, Notre Dame: Two-year starter after a red-shirt 2014 season. The Irish were 10-2 in the 2015 regular season, with two-point road losses to Clemson and Stanford, then skidded to 4-8 in 2016. Mechanics and footwork are an issue for Kizer, who otherwise has NFL size and tools.

Stats line: Two-year completion rate of 61.15 percent – but 59.3 in 2016 with 45-18 ratio of TDs to interceptions.

4. Patrick Mahomes II, Texas Tech: He thrived in his school's Air Raid offense as a starter his last two years. Accuracy is an issue, and he's regarded as a development project for a team that does not need an immediate starter. His father, Pat, was a Major League baseball pitcher for 11 seasons.

Stats line: 4,653 yards, 36 TDs, 15 Int in 2015. In 2016: 5,052 yards, 41 TDs, 10 Int. He tied the NCAA one-game record with 734 passing yards against Oklahoma in 2016.

5. Nathan Peterman, Pittsburgh: A two-year starter at Pitt (2015-16) after two seasons as a backup at Tennessee.

Stats line: He had only 23 attempts at Tennessee, but 619 at Pitt with a completion rate slightly above 60 percent with 47 TDs, 15 picks.

Others: Joshua Dobbs, Tennessee; Davis Webb, Cal; Brad Kaaya, Miami (Fla.); C.J. Beathard, Iowa; Chad Kelly, Mississippi; Jerod Evans, Virginia Tech.; Alek Torgersen, Penn; Trevor Knight Texas A&M.

Spotlight – Central casting: Cooper Rush of Central Michigan looks the part of a pro quarterback at 6-3 and 228 pounds. He compiled good stats in his five years at CMU, and he benefited from playing his last two seasons under John Bonamego, former special teams coordinator of the Lions.

Rush was the Chips' full-time starter from 2014-16 after starting the last 10 games of 2013.

Rush actually did exercises to help measure up when the scouts measured his hands at the Combine. The exercises must have worked. Rush's hands measured at 9-1.

"I looked up a YouTube video of hand stretching," Rush said at the Combine. "Just random, for people who type a lot, and did that."

Hand size couldn't have been much of a problem. He once threw seven TD passes in the Chips' win over Western Kentucky in the 2015 Bahamas Bowl.