The winger joined the Gunners on Friday from Brighton as part of a deal that could be worth up to £26million.
Arsenal believe they filed the paperwork before midday on Friday, meaning Trossard could be involved against United at Emirates Stadium.
“I’m really excited to get started,” Trossard said in his first interview with Arsenal.com. “This is a big club and I’m ready to show the fans what I can do.
“Everyone has seen how well we’re doing already and I’m here to help achieve their dreams – including myself.”
The Gunners are expected to name the same starting line-up that beat Tottenham 2-0 in the north London derby before Sunday’s game with United.
Gabriel Jesus is still out with a knee injury and Reiss Nelson has a hamstring problem, but everyone else is available to manager Mikel Arteta.
Predicted Arsenal XI (4-3-3): Ramsdale; White, Saliba, Gabriel, Zinchenko; Odegaard, Partey, Xhaka; Saka, Nketiah, Martinelli.
Sunday 4.30pm GMT, Sky Sports
Venue: Emirates Stadium
Referee: Anthony Taylor
Arsenal squad from: Hein, Ramsdale, Turner; Cedric, Gabriel, Holding, Saliba, Tierney, Tomiyasu, White, Zinchenko; Elneny, Lokonga, Odegaard, Partey, Saka, Smith Rowe, Trossard Vieira, Xhaka; Martinelli, Marquinhos and Nketiah.
Injured: Jesus (knee), Nelson (hamstring)
