The Dutchman is set to be in the stands for their game against Brentford tomorrow, meaning his first match in charge will be against West Ham on Tuesday.
On his Leicester arrival, Van Nistelrooy said: “I’m proud, I’m excited. Everybody that I speak to about Leicester City Football Club is enthusiastic.
“They have great stories about the quality of the people working at the club, the supporters and, of course, the recent history of the club is impressive.
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“I’m excited to start and to get to know everyone and give everything I can for the football club.”
Chairman Aiyawatt Srivaddhanaprabha added: “It is my pleasure to welcome Ruud to Leicester City.
“He joins a Club with a rich history, passionate supporters, and a talented squad, and we are all excited to see the impact he can have as we embark on this new chapter together.
“Ruud’s experience, knowledge, and winning mentality will undoubtedly bring great value to us, and we look forward to supporting him in achieving success for our fans and our club.”
During his spell as Man Utd caretaker, Van Nistelrooy twice beat Cooper’s men.
They met in the Carabao Cup on October 30, with the Red Devils running out 5-2 winners.
Leicester stars party in nightclub next to ‘Enzo I miss you’ sign hours after Chelsea loss on night before Cooper sacked
And he beat Leicester again 3-0 just 11 days later in the Premier League.
Cooper, 44, won just two of his 12 Prem encounters at the Leicester helm, having succeeded Enzo Maresca in the summer, who guided the club to the Championship title last term.
The players seemingly miss their old boss as they were spotted partying next to a sign that read “Enzo I miss u” during their Christmas party.
According to The Telegraph, Cooper fell out with Jannik Vestergaard, Harry Winks and Hamza Choudhury during his ill-fated 157-day stint in charge at the King Power, with the former even being banished from training at one stage
The Foxes are 16th in the Prem table, a point above the relegation zone.
Prior to joining Ten Hag’s Old Trafford coaching staff, the former Man Utd and Real Madridstriker managed PSV Eindhoven.
He won 33 of his 51 games in charge, winning the KNVB Cup in 2023.
Van Nistelrooy stepped down a week before the end of that season, citing a lack of support from above.