Johnny Manziel tells Jordan Rodgers that he's trying to focus on his daily regimen as he works out at Texas A&M's pro day. (2:04)

This is the window. Now is Johnny Manziel's best chance -- as slim as it might be -- to catch the eye of an NFL team before deciding whether to circle back and make a two-year commitment to play in the CFL.

The process began last week, when Manziel jumped into the University of San Diego's pro day attended by scouts from 13 NFL teams. It will accelerate on Wednesday as he joins the Spring League, a developmental program that runs March 28 through April 15 in Austin, Texas, with games staged on April 7 and 12 -- Manziel's first since starting for the Cleveland Browns on Dec. 27, 2015.

Manziel said last week "there's still people that still doubt what I'm doing and still doubt where I'm at" -- an acknowledgement of his extensive list of off-field indiscretions. He won't resolve all of those questions over a two-week minor league experience, but the stint will help him address a more tangible issue: How far, if at all, did he deteriorate physically during what he admits were long stretches of substance abuse?

There is no precedent for a quarterback returning from two years away to earn a starting job in his first season back. There have been only six cases since the 1970 merger in which a quarterback has started eight-plus games in a season after not playing in an NFL game over the prior two-plus seasons, according to the Elias Sports Bureau research, and each were either on a roster or played in the CFL in the interim:

Year GS QB Team Last played 2014 8 Drew Stanton Arizona 2010 2012 8 Brady Quinn Kansas City 2009 2006 8 Damon Huard Kansas City 2003 2003 8 Rick Mirer Oakland 2000 1998 10 Doug Flutie Buffalo 1989 1991 8 Erik Kramer Detroit 1987

And fair or not, NFL teams have recently demonstrated a resistance toward investing in backup quarterbacks who they believe will draw public attention.

The league itself has also changed dramatically since Manziel was last a part of it. More than half of teams (17) hired new head coaches in those two seasons. There are also 14 new general managers, 27 new offensive coordinators and 14 teams with new starting quarterbacks. A total of 65 quarterbacks have started at least one game since the end of the 2015 season.

If no NFL teams express interest based on his performances in the Spring League, however, Manziel would still have time to join a CFL team before the start of the league's training camp in May. His rights continue to be owned by the Hamilton Tiger-Cats, whose season begins June 16 and whose coach -- former Hawaii and SMU coach June Jones -- has said Manziel would be "the best player to ever play up here."

CFL rookies typically must sign contracts that bind them to the league for two seasons. Unless his CFL team grants a rare waiver, Manziel wouldn't be eligible to return to the NFL before November 2019 -- or, more realistically, the 2020 NFL season.

"If something [with the NFL] pops up, it pops up. And if not, if I don't get the opportunity to go back, I'm going to go play in the CFL, and things are going to be fine," Manziel said at Texas A&M's pro day on Tuesday. "One way or another, one day down the line, I'll get back to exactly where I want to be, because I'm not going to stop until I do."

How did the 2012 Heisman Trophy winner (and 2014 first-round draft choice) fall this far? Let's take a closer look at the 800-plus days since Manziel last played in the NFL.

January 2015: In Week 17 of the 2015 season, Manziel visits Las Vegas, wearing a wig to hide his identity, and misses a mandatory concussion treatment on the morning of the Browns' final game. In an interview with Uninterrupted's "The ThomaHawk Show" podcast last month, Manziel says: "What a complete lack of respect for an organization that was trying to stick by me," he says. "What just a completely selfish decision."

February 2016: Agent Erik Burkhart drops Manziel as a client, an unusual move that Burkhart says he made because "it has become painfully obvious that his future rests solely in his own hands." (Manziel re-signs with Burkhart in March 2017.)

March 11, 2016: Browns release Manziel, knowing at the time they would still be responsible for his guaranteed base salaries of $1.169 million in 2016 and $1.004 million in 2017.

April 2016: It becomes public that Nike has terminated Manziel's endorsement contract.

May 2016: Photographs emerge of a gaunt and pale Manziel on the pool deck of a Las Vegas hotel.

Not even cracking a joke here, but Johnny Manziel doesn't look well to me pic.twitter.com/fisOYl9UW2 — Jemele Hill (@jemelehill) May 20, 2016

July 2016: Manziel posts photos and videos to his own Instagram account, with Hawaii tagged as the location, of his notably gaunt appearance.

September 2016: Manziel enrolls in classes at Texas A&M.

September 2016: Technically served a four-game suspension in 2016 for violating the NFL's substance abuse policy, even though he was not on a roster. Any interested team knows that he is one positive test away from a yearlong suspension.

December 2016: Reaches agreement to have charges dropped of domestic abuse against his former girlfriend, Colleen Crowley, if he met certain conditions. The NFL did not add discipline under its personal conduct policy.

January 2017: Tells ESPN that he is sober after years of heavy alcohol and drug use. At about this time, according to a later interview with ABC News, Manziel is diagnosed with bipolar disorder. He begins treatment.

February 2017: Works with high school quarterbacks at an Elite 11 camp in Miami.

August 2017: Says he would consider coaching if he can't find a way back into football as a player.

August 2017: Works out for Hamilton officials in Buffalo. Tiger-Cats executive Kent Austin says Manziel looked "fine" but was not ready to be signed.

September 2017: Manziel and his agent initiate the process of negotiating a CFL contract, beginning with an expression of interest with the Tiger-Cats.

Sept. 15, 2017: CFL commissioner Randy Ambrosie steps in, extends the negotiating period and prohibits the Tiger-Cats from executing a contract pending a "process for evaluation of the player." Manziel and Ambrosie meet later that month.

November 2017: Photographs emerge on TMZ of Manziel at a beach in Hawaii with his girlfriend, Bre Tiesi, in what becomes known on social media as a "Dad Bod."

December 2017: The Tiger-Cats' June Jones says: "I think he'd be the best player to ever play up here. He can throw it and he can run it like nobody ever has been able to do."

Dec. 13, 2017: Ambrosie tells ESPN that he found Manziel to be "thoughtful ... authentic and sincere" during their September meeting.

Dec. 28, 2017: Ambrosie gives permission for Tiger-Cats to sign Manziel.

Jan. 7, 2018: Hamilton acknowledges it has made Manziel a qualifying offer, allowing it to retain his rights while negotiating continues.

Jan. 8, 2018: Agent Erik Burkhart calls the offer a "place holder" and gives the Tiger-Cats until Jan. 31 to make an offer that is fair and comparable to what they have paid their quarterbacks in the past. Their 2017 starter, Zach Collaros, received a league-high $500,000 Canadian, which is currently worth about $387,000 in U.S. currency.

Jan. 31, 2018: No deal is reached. Hamilton says in a statement that it will continue its "due diligence" on Manziel.

Feb. 12, 2018: ABC airs interview on "Good Morning America" in which Manziel confirms the bipolar disorder. Of his mental state before diagnosis he says: "You are left staring at the ceiling by yourself and in that depression and back in that dark hole of sitting in a room by yourself, super depressed, thinking about all the mistakes you made in your life. What did that get me? Where did that get me except out of the NFL? Where did that get me? Disgraced."

In an interview with @GMA, Johnny Manziel said he has been diagnosed as bipolar and is taking medication for it.



His goal is to get back on the football field. pic.twitter.com/pYobONAEWs — SportsCenter (@SportsCenter) February 12, 2018

Feb. 14, 2018: The Spring League announces Manziel's participation.

March 2018: Manziel and Tiesi are married in a private ceremony.

March 22, 2018: Throws during University of San Diego pro day, says that he is a "different person" and that he has had more than a year of "solid" behavior and workout regimen. "I feel like if I can parlay that into enough months and, people will be able to buy into that and trust what I'm doing again, that I'm not just trying to pull a fast one to get back into the NFL."