Arsenal manager Mikel Arteta's worst fears have been realised after it was confirmed Gabriel Jesus is set to be sidelined for the rest of the season with a knee injury.

The Gunners have confirmed that Jesus - who has scored six times across his past seven appearances - ruptured the anterior cruciate ligament in his left knee when landing awkwardly in his side's FA Cup defeat to Manchester United on Sunday.

The devastating injury is likely to keep Jesus out for much of 2025.

The news leaves them with only one recognised forward in Kai Havertz, with star man Bukayo Saka out until March at the earliest with a hamstring tear.

Jesus' injury will place fresh impetus on Arsenal's activity in this month's transfer window and even greater focus on Havertz.

Arsenal are investigating abusive social media posts sent to the Germany international's wife Sophia following his penalty shootout failure against United, which followed several mises during the match.

"We really have to do something about it, because accepting that and hiding this has terrible consequences," Arteta said.

"It's something we have to eradicate from the game because it's so cynical and dependent to a result of an action. There is no other industry like this."

Arteta confirmed he is looking for players to fill his depleted side, with a No.9 even more of a priority.

Meanwhile, a former Arsenal academy striker has joined Aston Villa.

Borussia Dortmund's Netherlands international Donyell Malen, 25, has joined for a fee reported to be in the region of 21 million sterling ($A41 million).

Malen joined Arsenal's academy from Ajax in 2015, but headed home to PSV Eindhoven in 2017 without making a senior appearance for the Gunners.