Lukáš Klein (born 22 March 1998) is a Slovaktennis player. Klein has a career-high ATP singles ranking of World No. 236, achieved on 1 November 2021. He also has a career-high doubles ranking of World No. 240, achieved on 5 April 2021.[2]
Klein has reached 10 career singles finals, with a record of 6 wins and 4 losses all on the ITF Futures Tour. Additionally, he has reached 11 career doubles finals, with a record of 5 wins and 6 losses, including a 1–3 result in ATP Challenger finals. He won the doubles title at the 2021 Challenger La Manche with compatriot Alex Molčan1–6, 7–5, [10–6].
2021: ATP debut, top 250 and Olympics singles and doubles debut[]
Klein made his ATP main draw singles debut in March 2021 at the 2021 Argentina Open in Argentina, where he defeated Andrea Collarini, Thiago Seyboth Wild and Ernesto Escobedo to qualify for the main draw. Klein then went on to upset compatriot Andrej Martin in the first round defeating him 7–5, 6–3. He would go on to lose in the second round to top seed, local favourite and eventual champion Diego Schwartzman in straight sets 4–6, 2–6.[3] He reached the top 250 and a career-high of World No. 248 in singles on 28 June 2021 after reaching the second round also as a qualifier at the 2021 Mallorca Championships by defeating 8th seed Dusan Lajovic.
At the Olympics, Klein was entered as an alternate for Matteo Berrettini, who had withdrawn due to a thigh injury.[4][5] He also participated in the doubles event partnering Filip Polášek where they reached the second round.
Slovakia
Gregoire Jacq
Patrik Rikl
Jacopo Berrettini
Daniel Michalski
Jakub Paul
Fabian Marozsan
Kirill Kivattsev
V. Alekseenko 
F. Ferreira Silva
H. Callahan 
Joran Vliegen 
Uladzimir Ignatik
Harri Heliovaara 
Blaz Kavcic 
Alex De Minaur
16)
7)
