Ondrej Duda (Slovak pronunciation: [ˈɔndrej ˈduda]; born 5 December 1994) is a Slovak professional footballer who plays as a midfielder for Saudi Pro League club Al-Ettifaq and the Slovakia national team.

Duda began his football career at his hometown club MFK Snina. He later moved to Košice, where he rose through the youth team ranks, making his first-team debut for the club at the age of 17 as a late substitute during a 1–0 home win against Slovan Bratislava.

In the winter of 2013–14, Duda decided to not extend his contract with Košice, which would expire the following summer. In February 2014, Duda then joined Legia Warsaw on a four-and-a-half-year deal.

On 30 July 2015, Duda was hit by a stone in Legia's UEFA Europa League qualifier away at Kukesi in Albania, being stretchered off and the match abandoned. The game was awarded as a 3–0 Legia victory and their opponents were fined €70,000 and forced to play their next European home match behind closed doors.

On 20 July 2016, Duda signed for Bundesliga side Hertha Berlin on a five-year deal. After being sidelined with a knee injury shortly after signing and also undergoing knee surgery in November 2016, Duda made his competitive debut for Hertha on 25 February 2017 in a 2–0 win over Eintracht Frankfurt as an 89th-minute substitute, 7 months after signing with the club. Duda famously scored against Bayern Munich, as he smashed home a cross into the roof of the Bayern net, past a helpless Manuel Neuer. Duda's goal was Hertha Berlin's second goal against Bayern, as the Slovak international inspired the Berliners to a 2–0 victory over the German champions.

Duda experienced a good year with Hertha in the 2018–2019 season. He played in 32 of the 34 Bundesliga games, scoring 11 goals and adding 6 assists. Even though Hertha had failed to qualify for any European competitions in the subsequent season, finishing 11th and 11 points behind Europa League positions, Duda was spotted and inquired about by Sevilla, as reported in mid-May 2019. Sevilla was to send an offer to Berlin, even meeting with Duda's father. Hertha manager Pal Dardai was full of praise for the excellent Duda, saying the following about the world class Slovak playmaker, "Duda can do things with the ball that very few here can".

Duda's 2019–2020 season with Hertha was not as good, as the previous one. Duda started the season with a new manager. Pál Dárdai, who led Hertha from the time of Duda's arrival, was replaced over the summer by Ante Čović. He was fielded in the starting line-up in the first five rounds of Bundesliga, following the trend from last seasons. Of the following twelve games, however, Duda only starred in two, recording a total of just over 94 minutes in these matches against Hoffenheim and Eintracht Frankfurt. Appointment of Jürgen Klinsmann, a former World Cup winner and a successful international manager, on 29 November 2019, was traced to be a partial reason for Duda's absence from the first team. After Duda was left off the bench for four games, being relegated to reserves for one of them, it was revealed that Klinsmann did not include Duda in his plans for Hertha, despite Duda's intention to remain with the side. Duda was subsequently free to look for a different club. Before his departure, Duda was fielded in seven Bundesliga games and two Pokal fixtures. He scored his only goal in a cup fixture against Dynamo Dresden.

Duda was loaned to Norwich City for the rest of the 2019–20 season on 12 January 2020. He had commented, that he intends to be entertained by the game again and is happy about a move to an even better league, hoping for notable play-time.