Pep Guardiola says Rodri will be out "for a long time" because of a knee injury he suffered against Arsenal, but the Manchester City manager is retaining hope it could be "less than expected."

The midfielder has travelled to Barcelona for tests after being forced off in the first half of Sunday's 2-2 draw at the Etihad Stadium.

He is set to undergo surgery, but Guardiola says a decision has not yet been made about what type of operation he needs.

Sources have told ESPN that, depending on the final decision taken by medical staff, Rodri could be out for between five and eight months.

"Still we don't have the definitive [answer]," Guardiola said at a news conference on Tuesday.

"He will be out for a long time. But there are some opinions that it will be less than we expect. Right now I cannot tell you. We are waiting for the last phone calls and the type of surgery he needs. Tonight or tomorrow we know."

Rodri's prolonged absence is a major blow to City, who are aiming to win their fifth successive Premier League title.

He has been a key member of Guardiola's squad since arriving from Atletico Madrid in 2019 and helped Spain win the European Championship in the summer.

The 28-year-old is one of the favourites for the Ballon d'Or along with Real Madrid winger Vinícius Júnior.

"We will have a good season," Guardiola added.

"I trust a lot in my players. I have a duty to find a solution. He's irreplaceable, when you don't play with the best player in the world. My duty is to find a solution, be competitive like many years and continue to be there."

Guardiola was speaking after City booked their place in the fourth round of the Carabao Cup with a 2-1 win over Championship side Watford.

Jérémy Doku scored in the fourth minute when Watford got it wrong trying to pass out from the back.

Matheus Nunes made it 2-0 before half-time with his first City goal.

The Portugal midfielder, handed a rare start in a much-changed team for City's second game in just over 48 hours, arrowed a shot into the corner from the edge of the area.

City were in control for much of the night and could have scored more, although Watford ensured a nervous end when Tom Ince scored four minutes from time.