Léo Joseph Paul Westermann (born 24 July 1992) is a French professional basketball player who is currently playing for the Crailsheim Merlins of the German Bundesliga. Standing at 1.98 m (6 ft 6 in), he plays the point guard position. He also represents the senior French national basketball team.
 Westermann started his men's club career in 2008, playing for Centre Fédéral de Basketball, in the Nationale Masculine 1, the third division of French basketball. He played for Centre Fed for two seasons, averaging 10.1 points, 2.6 assists, and 1.1 steals per game, in 48 games played.
 He is a big fan of KK Partizan.
 Westermann signed with the French club ASVEL Basket, in 2010. He stayed there for two seasons, playing in the top-tier level French Pro A and in the European-wide 2nd-tier level EuroCup. In 2012, Westermann was selected to play for the World Team at the Nike Hoop Summit in Portland, Oregon. He left the team just a few hours before he signed a contract with a different team.
 On 2 July 2012, it was reported that Westermann had signed a three-year contract with Serbian club Partizan Belgrade. With Partizan was one of the candidates for the prestigious EuroLeague Rising Star award, which eventually went to Kostas Papanikolaou. In his first season, he averaged 9.6 points, 2.6 rebounds, and 4.1 assists per game in the EuroLeague. In the ABA League season, Westermann helped his team to win the title, averaging 6.9 points, 2.5 rebounds, and 2.2 assists per game, in 28 games. In November's EuroLeague away game against CSKA Moscow, he tore his ACL on his knee, which sidelined him for the remainder of the season. As a result of the injury, Partizan had to find a replacement for him in Milenko Tepić, a former member of the team.
 On 17 July 2014, Spanish club FC Barcelona acquired the player rights of Westermann. On 25 July 2014, he was loaned by Barcelona to the French EuroLeague team Limoges CSP, for one season. Over 10 EuroLeague season games, he averaged 7.7 points, 2.3 rebounds, a career-high 4.3 assists, and 1.3 steal per game. On 11 July 2015, Westermann signed a one-year extension, with the option of another year, with Limoges.
 On 30 May 2016, Westermann signed a one-year contract, with the possibility to extend it for one more year, with the Lithuanian club Žalgiris Kaunas. Over 30 EuroLeague season games, he averaged 8.2 points, 3.2 rebounds, 5.5 assists, and 0.5 steals per game.
 On 22 June 2017, the Russian club CSKA Moscow, announced the signing of Westermann, to a 1+1 (2nd year being optional) year contract. On 16 July 2018, Westermann was officially released from CSKA.
 Westermann returned and signed with Žalgiris Kaunas on 23 September 2018.
 On 12 July 2019, Westermann signed a two-year deal with Fenerbahçe of the Turkish Basketball League. On 22 December 2020, he was released by Fenerbahçe.
 On 22 December 2020, Westermann signed as a free-agent with EuroLeague powerhouse FC Barcelona of the Liga ACB.
 On 29 July 2021, Westermann signed a one-year deal with EuroCup champions AS Monaco Basket of the French LNB Pro A and the EuroLeague.
 On 5 August 2022, Westermann signed a one-year deal with Monbus Obradoiro of the Liga ACB.
 In late September 2023, he signed with the Crailsheim Merlins of the German Bundesliga.
 As a player of France's junior teams, Westermann won a silver medal at the 2009 FIBA Europe Under-18 Championship. Westermann also played at the 2011 FIBA Europe Under-20 Championship, where he helped France to win a bronze medal. At the 2012 FIBA Europe Under-20 Championship, Westermann won the silver medal, and was named the tournament's MVP.
 Westermann was on the senior French national basketball team's candidate list to compete at the EuroBasket 2013. However, unlike his teammate in Partizan Belgrade, Joffrey Lauvergne, he did not make it onto France's final 12-man squad for the tournament. He played with France at EuroBasket 2015, where he won a bronze medal.
 He also played at EuroBasket 2017.