That may seem like an outlandish claim after one game, and one which the Niners had a chance to tie on the final drive against a team many perceive as a Super Bowl favorite.
However, the correlation between going 0-2 and missing the playoffs is clear. Per Optimum Scouting's Justis Mosqueda, since 2009 only six (8.5%) of the 77 teams to start the season with an 0-2 record made it to the playoffs.
As Mosqueda points out, a 10-6 record is usually what is required to reach the playoffs, and the numbers back this up. Per The Football Outsiders Almanac, 9-7 teams historically make the postseason 45.9 percent of the time, with the figure increasing to 80.6 percent for 10-6 teams.
Qualifying for the playoffs therefore essentially requires going 10-4 the rest of the way, and that would be a daunting task for the Niners, whose schedule features just five teams that had losing records in 2017.
Dropping to 0-2 would also put the 49ers in danger of falling into an even greater hole with challenging road games to come against the Kansas City Chiefs and Los Angeles Chargers in Weeks 3 and 4, respectively.
But a potential defeat against the Lions would be more worrying for the 49ers because of the message it would send about this team.
San Francisco wasted numerous opportunities to be in a position to beat one of the best teams in the NFC and emerges from Week 1 with credit for keeping it close against the Vikings. Yet if the Niners are unable to beat a Detroit team making a long journey west on a short week after a blowout loss to the New York Jets -- and one reportedly already at odds with its new head coach -- then serious questions will be asked of a young San Francisco roster that is expected to take another step forward this season.
On the surface it appears ridiculous to label any Week 2 NFL game "must-win", especially after the New Orelans Saints recovered from such a start to get agonizingly close to making the NFC Championship game last season. History, though, is against the 49ers making such a turnaround and the Lions are the type of team that San Francisco should be looking to beat with relatively little difficulty in year two of the Kyle Shanahan and John Lynch era. Sunday's home opener may not be "must-win", but it's as close as it gets.