Jesus suffered the injury while playing for Brazil against Cameroon in Qatar and is set for up to three months out after undergoing surgery.
The 25-year-old has played an instrumental role in Arsenal's rise to the top of the Premier League table, scoring five goals and providing five assists in 14 appearances.
Any prolonged absence for Jesus is likely to have an impact on Arsenal's title charge, which sees them five points clear of second placed Manchester City.
"I spoke with him straight after the Cameroon game. We have the contact between each other, with all the players we have here in the World Cup," Xhaka told reporters.
"It's a shame because you saw in the first round of the Premier League how important he is for us. I don't know how big the injury is, maybe two or three months, I think.
"But he is a strong guy. It’s a small injury for him I think, and we will support him. He knows that we are behind him and hopefully we can get him back as quick as possible."
Jesus' injury is likely to pave the way for Nketiah to have a run in the side.
The Englishman has made 12 substitute appearances without scoring in the top flight this season but had strong finish to the 2021/2022 season, scoring five goals in Arsenal's last seven games to earn a new contract.
Xhaka believes Nketiah will prove to be an adequate replacement for Jesus.
"We have the option with Eddie, of course. He showed great games as well in the past and we need to support Gabi first," he added.
"We need to support Eddie as well, because he will be a big, big part of the next two or three months. But I am looking forward because we have the quality to bring Eddie there and to help him.
