Mikel Arteta says Arsenal are "very worried" by the extent of the injury suffered by striker Gabriel Jesus.

The Brazil international limped off during the early stages of Sunday's FA Cup defeat by Manchester United, with what the club fears is an anterior cruciate ligament rupture.

Arteta says Arsenal are waiting for clarification on the prognosis, but the head coach could not hide his concern for the forward.

"[It's] not looking good at all, but we need to review with the specialist and will have more information this afternoon," he told reporters ahead of Wednesday's North London derby against Tottenham.

"I don't want to confirm anything until we have the final report this afternoon. We were very worried straight after the game, and we are very worried today."

With Jesus joining the likes of Bukayo Saka and Ethan Nwaneri in the treatment room, Arteta acknowledged the club are "actively looking" for new players in the transfer window.

"My answer doesn’t change," he added. "We are actively looking into the market to improve the squad. We always have been. It would be naive not to. We are looking, and we are trying, so let’s see what we can do."

The Spaniard also defended Kai Havertz who, along with wife Sophia, was subjected to vile abuse on social media after he missed the decisive penalty in the shootout loss to Man Utd.

"It's incredible, honestly," he said. "We really have to do something about it, because accepting that and hiding this has terrible consequences. 

"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. When we played Ipswich [Town] on December 27, we won 1-0 and Kai Havertz scored. The whole stadium after that is singing the 'Waka, Waka' [his chant]. That was 20 days ago. Where is the perspective?

"We are all responsible. That's a really serious matter. It affects me. It affects him and everybody that is in the industry.

"We can accept it and say: 'that's our job', but there are certain limits and the line has to be drawn. We put a lot of attention on technology and what is next in football. What is next in football is that this should be prohibited. It cannot happen. That's it."