NFL preseason 2015 schedule: Big tests for Marcus Mariota, Cam Newton on Friday night

The action starts at 7:30 p.m. ET with the Carolina Panthers hosting the defending Super Bowl champions. Both teams are adjusting to potentially critical losses -- the New England Patriots could be without Tom Brady for as many as four regular season games, while the Panthers are trying to patch up an offense that lost star wide receiver Kelvin Benjamin to a season-ending ACL tear.

The next matchup features the Detroit Lions and the Jacksonville Jaguars at 8 p.m. ET on CBS, one of five nationally televised games this week. The Lions are coming off a strong defensive performance against Washington last week, when they absolutely dominated Robert Griffin III and the Hogs' offensive line. This game will be a good test for Jaguars quarterback Blake Bortles, who has looked much more confident in the pocket this preseason.

Friday's final game is also set to kick off at 8 p.m. ET, with Marcus Mariota and the Tennessee Titans traveling to Arrowhead Stadium to face the Kansas City Chiefs. Mariota has shown steady improvement in his first two preseason games and has impressive poise for a rookie. But he hasn't yet faced a pass rush as formidable as the Chiefs, who last year ranked fifth in the league in sacks.

Here are some things to watch for Friday night. For full listings of the games, visit 506sports (all times Eastern):

The Patriots still don't know who they'll have under center in Week 1 of the regular season, but if it has to be Jimmy Garoppolo, they should be encouraged by a bounce-back performance from the young quarterback in his second preseason game last week. He completed 28 of 33 passes for 269 yards and one touchdown against the Saints, and this week he'll look to get important reps with recently signed veteran Reggie Wayne and the rest of the Patriots' receiving corps.

Carolina's offense looked sluggish last Saturday in its first game without Benjamin (zero first downs and 8 yards in the first quarter), but look for it to be improved this week with wide receiver Devin Funchess expected to return after sitting out last week with a tight hamstring. Tight end Greg Olsen is now most likely the focus of the Panthers' receiving game, but Carolina still needs the second-round pick to learn quickly and become a dependable target this season.

Bortles took a step back in the accuracy department last week against the Giants, completing just 8 of 16 passes. Although his wideouts dropped a few balls, there were some miscommunication issues and Bortles clearly was off target on several attempts. One key player to watch in this game is second-round pick T.J. Yeldon, who is expected to get his first NFL carries after sitting out the first two preseason games.

The key number from Mariota's performance last Sunday night was zero -- the number of turnovers that he had against the Rams. Already showing the unflappability of a veteran, the rookie needs to continue to improve his pocket passing and protect the ball in this game. Elsewhere on offense, the No. 1 running back job appears to still be up for grabs, with Bishop Sankey struggling and David Cobb emerging as a legitimate threat to get significant snaps.