Kassem El Zein

Al-Mina'a

On 28 January 2020, El Zein was sent on a three-month loan to Iraqi Premier League side Al-Mina'a. He made his debut on 17 February 2020, in a 1–0 home win over Naft Al-Janoob in the first matchday of the season. El Zein played four league games for Al-Mina'a; however, the season was cancelled due to the COVID-19 pandemic.

Al-Nasr

On 18 June 2020, El Zein was sent on a one-year loan to Kuwaiti club Al-Nasr. He made his debut on 16 October, in a 2–1 win against Al-Shabab in the classification league between Kuwait Premier League and Kuwaiti Division One clubs. El Zein helped his side finish first in the qualifying stage. His debut in the 2020–21 Kuwaiti Premier League came on 22 January 2021, in a 1–0 away win against Al-Shabab. El Zein scored a goal on 25 April, helping his side to a 2–1 away win against Al-Fahaheel. He finished the season with 17 league games.

Nejmeh

El Zein returned to Nejmeh for the 2021–22 season. His contract was renewed in 2022. On 30 June 2024, El Zein scored the decisive goal in the 95th minute in the last game of the 2023–24 Lebanese Premier League against rivals Ansar, allowing Nejmeh to win the league for the first time in 10 years.

El Zein was first called up to the Lebanon national team in October 2014, as part of a mixed squad of senior and Olympic players for friendly matches against Qatar and Saudi Arabia. He made his on 14 October 2014, against Saudi Arabia. In December 2018, he was called up for the 2019 AFC Asian Cup, where he played a group stage game against Saudi Arabia. El Zein scored his first international goal against India on 10 September 2023, to help Lebanon finish third in the 2023 King's Cup. In December 2023, El Zein was included in the Lebanese squad for the 2023 AFC Asian Cup. Following Lebanon's missed qualification to the 2027 AFC Asian Cup, following a 2–0 defeat to Yemen on 4 June 2026, El Zein announced his retirement from the national team.

Initially starting out as a full-back, El Zein progressed into a centre-back with the years; his main abilities are his tackling and reading of the game.

As of 2019, El Zein was working as a part-time chef at L'Avenue Du Parc, a restaurant in Beirut. He stated that "while in other countries football can be a full-time job, in Lebanon it is necessary for a player to have a second job." El Zein's favourite club is Manchester United, while his favourite player is former Manchester United defender Nemanja Vidić.