The 29-year-old, who had spells at Fulham and Southampton, returns to English football after making 58 appearances since 2021 for Nice.
Paris St Germain are contemplating legal action after some of their supporters were involved in violent crowd trouble in Nice ahead of a Europa Conference League match between the Azurean side and Cologne on Thursday.
Italy striker Mario Balotelli is hoping to get back on track as he joined Olympique de Marseille from fellow Ligue 1 side Nice on a six-month contract on Wednesday.
Seri, who had also been linked to Chelsea and Borussia Dortmund, joined Nice in 2015 from Portuguese side Pacos de Ferreira.
Vieira began his coaching career with Manchester City's youth team before joining New York and guiding them to successive playoff appearances.
Dortmund parted ways with coach Peter Stoeger at the end of the season after the club finished fourth in the Bundesliga.
Italian striker Mario Balotelli on Saturday dropped a strong hint he could leave Nice at the end of the season after two years with the Ligue 1 club.
The agent is convinced that the player "has matured" and that he is ready to face a new stage in his football career.
AC Milan, Villarreal and Nice reached the knockout stage of the Europa League after posting wins on Thursday in the penultimate round of the group stage.
Paris St Germain went a provisional seven points clear at the top of Ligue 1.
Vehicle attacks of the sort seen in Barcelona are easy to organise and difficult to stop and have become part of a new reality for Europeans, experts say.
Nice mayor has said he will convene European counterparts next month to see how they can improve security in the aftermath of Thursday's van attack in Barcelona.