Premier League leaders Arsenal signed Belgium forward Leandro Trossard from Brighton on Friday in a deal worth a reported £27 million ($33 million).
The 28-year-old could make his debut for Mikel Arteta's side, who are five points clear at the top, in Sunday's crucial clash against Manchester United at the Emirates Stadium.
"It is good work from everyone at the club to complete the signing of Leandro. He is a versatile player with high technical ability, intelligence and a great deal of experience in the Premier League and at international level," Arteta told Arsenal's website.
"Leandro strengthens our squad as we head into the second part of the season and we're all looking forward to working with him. We welcome Leandro and his family to Arsenal Football Club."
Arsenal sporting Director Edu said: "We're delighted to have completed the signing of Leandro Trossard. We have a clear plan and strategy for our direction, and it's been a great team effort in bringing Leandro to the club.
"Leandro is a player who will give us a high level of quality going forward. I know Mikel and our coaches are excited to start working with him."
Arsenal were pipped to the signature of Ukraine winger Mykhailo Mudryk by London rivals Chelsea last weekend.
Trossard, who played for Belgium at the recent World Cup, scored seven times in 16 Premier League matches for Brighton this season, including a hat-trick at Liverpool in October.
The winger's four-year spell at Brighton ended acrimoniously after his agent requested a transfer following a row with Albion manager Roberto De Zerbi.
De Zerbi said former Genk player Trossard "disappeared" from training after being told he would not be playing in Brighton's FA Cup tie against Middlesbrough earlier in January.
Trossard was subsequently left out of the squad for Brighton's Premier League match against Liverpool last weekend, which they won 3-0.
De Zerbi said: "I'm sorry for the last period, but I still would like to wish Leandro good luck for the future."