Trossard has agreed personal terms with the Gunners over a reported £90,000-a-week contract that runs until 2026 and contains the option for a further 12 months.
The 28-year-old is finalising the move on Friday and Arsenal are working hard to get it done by midday, so he could make his debut against United at Emirates Stadium on Sunday.
Arsenal will pay Brighton £21m up front for Trossard, with a further £5m coming in the form of add-ons. The Gunners have worked on a move for the Belgian quickly and turned to him after a deal for Mykhailo Mudryk failed last week.
Arsenal had been in talks with Shakhtar Donetsk over a deal worth over £60m for the winger, but Chelsea blew them out of the water to sign him for £88.5m. The Gunners swooped for Trossard after that, opening talks with Brighton this week and quickly agreeing a fee.
Arsenal have a good relationship with the club after buying Ben White in the summer of 2021 for £50m. Trossard had six months to run on his Brighton contract, although the club had the option to extend it by a year. The Belgian had refused to sign a new deal and his agent said this month that his client felt he had been “humiliated” by manager Roberto De Zerbi.
Trossard had been dropped from Brighton’s match-day squads and De Zerbi is happy a solution has been found.
“The situation was difficult I think, because I understood he wanted to leave,” said De Zerbi ahead of Brighton’s clash with Leicester. “I’m sorry for the last period because I prefer when people are clear not when there is some different behaviours.
“I think anyway we are a good team and we can play well with Leo or without Leo. In the transfer market, you can always improve. You can always buy new players but we are at a good level now and the players are very good players. It's not so easy to improve this squad. But if there is the possibility with (chairman) Tony (Bloom) and the club, we will do something."