Following four collegiate seasons at Florida State, Mann was selected by the Clippers with the 48th pick in the 2019 Draft. The 6-foot-5 shooting guard made his league debut during the second game of the season, a 19-point win over the Warriors on Oct. 24, posting one rebound. Mann scored his first points three games later, racking up four points, five assists, three rebounds and one steal in 10 minutes. On Nov. 16 in a win over the Hawks, the rookie had his first double-digit scoring effort (13 points) while also contributing eight assists and six rebounds. He swiped a season-high two steals during a win over the Grizzlies on Nov. 27 -- a mark he'd reach one more time during the season. About two months later on Jan. 22 against the Hawks, Mann blocked a season-high two shots. The rookie's best performance of the season occurred during the final game of the regular season, which was seeding play during the NBA bubble following the league's hiatus due to COVID-19. In that contest -- a win over the Thunder on Aug. 14 -- Mann produced season highs in points (25), rebounds (14) and assists (nine) while matching his season highs in steals (two). During the playoffs, Mann saw 27 minutes and totaled four points, seven rebounds, one assist and one steal. Overall, during the regular season, Mann averaged 2.4 points, 1.3 rebounds and 1.3 assists in 8.8 minutes.