Javier Manquillo was forced off against Cardiff City with an ankle injury.
The Newcastle United defender was handed a start after DeAndre Yedlin – Rafa Benitez's other senior right-back – was ruled out of this afternoon's game.
Yedlin suffered a knee injury in the club's season-opener against Tottenham Hotspur last weekend, though Benitez is hopeful that he will be fit for next Sunday's home game against Chelsea.
Manquillo went down clutching his ankle late in the first half.
The 24-year-old was withdrawn at the break and replaced by midfielder Isaac Hayden, who was later dismissed for a tackle on Josh Murphy.
Manquillo, however, was able to walk out of the Cardiff City Stadium without the aid of a crutches and he was not wearing a protective boot.
United manager Benitez said: "Yedlin will be fine. Hopefully, Manquillo, his ankle, will not be too serious. If we need to manage, we will manage. But it was difficult during the game."
Benitez still plans to loan out 22-year-old right-back Jamie Sterry, who had a spell at Crewe Alexandra last season.
Asked if the injury to Manquillo would have an impact on his plans for Sterry, Benitez said: "I don't think so."