Liverpool defender Trent Alexander-Arnold is a doubt for Sunday's Premier League game against champions Manchester City due to a groin injury, manager Juergen Klopp said on Tuesday.

The 22-year-old right back suffered a groin problem during training on Monday and did not make the trip to Portugal for Liverpool's Champions League group game against Porto.

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"It was shortly after training (on Monday), Trent went in a little bit earlier but didn't look serious. We did further assessment and in the end it was serious," Klopp said before the game at the Estadio do Dragao.

"He didn't travel with us. And it doesn't look great for the City game as well. It's a muscle thing. We thought it was tight, that he was just a bit tired from the (Brentford) game but it was more and now we have to deal with that."

Liverpool, the only team to remain unbeaten in the Premier League this season, is top of the standings with 14 points, one ahead of Pep Guardiola's City in second.