He decided not to play in the 2017 TaxSlayer Bowl with the rest of the Louisville team due to persistent injury issues during the season.

[8] On March 29, 2018, Alexander participated at Louisville's pro day, but opted to stand on his combine numbers and only performed positional drills.

[16][17] Throughout training camp, Alexander competed to be a starting cornerback against Davon House, Tramon Williams, Kevin King, and Josh Jackson.

[18] Head coach Mike McCarthy listed Alexander the fourth cornerback on the depth chart to start the regular season, behind Davon House, Kevin King, and Tramon Williams.

[19] On September 9, 2018, Alexander made his professional regular season debut in the Green Bay Packers' season-opener against the Chicago Bears and recorded three solo tackles during their 24–23 victory.

[20] On September 16, 2018, Alexander recorded eight combined tackles and was credited with half a sack during a 29–29 tie with the Minnesota Vikings in a Week 2.

[21] During the fourth quarter, Alexander intercepted a pass by Minnesota Vikings quarterback Kirk Cousins, but the play was negated due to a roughing the passer call on teammate Clay Matthews III.

[22] On September 30, 2018, Alexander made one solo tackle, broke up a pass, and made his first career interception off a pass thrown by Bills' quarterback Josh Allen, that was intended for wide receiver Zay Jones, before he sustained an injury and subsequently exited in the fourth quarter of a 22–0 win against the Buffalo Bills.

[25] In Week 8, he produced seven solo tackles and a career-high five pass deflections as the Packers lost 27-25 at the Los Angeles Rams.

He finished with a total 66 combined tackles (61 solo), 11 pass deflections, one interception, and was credited with half a sack in 13 games and 11 starts.

[27] On January 8, 2019, the Green Bay Packers announced the official hiring of Tennessee Titans' offensive coordinator Matt LaFleur as the new head coach.

[28] In week 5 against the Dallas Cowboys, Alexander recorded his first interception of the season off Dak Prescott and returned it for 37 yards in the 34–24 win.

[37] In the NFC Championship against the Tampa Bay Buccaneers, Alexander intercepted two passes thrown by Tom Brady during the 31–26 loss.