Eddie Howe is hopeful Kieran Trippier will return before the end of the season after a successful operation on his foot injury on Thursday.
The Newcastle right-back picked up the injury in the game against Aston Villa last week. He scored the only goal in that game and also struck in his side's win against Everton earlier in the week.
However, he had to leave the pitch during Sunday's game after a break in his left foot.
Howe has now expressed his hope that the England international will be back before the end of the campaign.
He said: "He had his operation yesterday and that went well, so that was good news.
"I don't know at this moment in time how long he will be out. Obviously we hope to have him back before the end of the season but it's a significant injury and a big blow to us because he was performing so well."
Asked whether he had a timeline on Trippier's recovery, Howe added: "No. As I say, we hope to see him before the end of the season but in terms of a definitive time, no. We have to see how his early rehab goes. The operation was a success. It's an opportunity now for somebody else to step up in his place, but certainly we're going to miss his leadership skills on the pitch and everything he was delivering for us.
"He's scored two goals in the last two games, which have been defining moments for us. But we're confident we have enough quality in the squad to cover."
Newcastle, who have climbed to 17th, face West Ham on Saturday.
(Photo: Robbie Jay Barratt – AMA/Getty Images)
How big of a blow is his absence to Newcastle?
A huge blow. In little more than a month, Trippier has become a leader, talisman and even a source of goals — his dramatic impact on the team and club cannot be overstated.
Full-backs are essential to the way Howe wants Newcastle to play and Trippier enjoyed the most touches in the side during the Everton game and built attacks, as well as scoring free kicks in successive matches.
Players and staff alike have spoken both on and off the record about the effect Trippier has had behind the scenes and he will be difficult to replace in the team.
Who could step up in his place?
The options are diminishing. Javier Manquillo's ankle injury has been described as "not serious" but he will not play against West Ham.
Beyond Manquillo, Emil Krafth is the right-back reserve option, but has rarely convinced at Premier League level, while Jacob Murphy has played at full-back on occasion, though he is a winger by trade.
Encouragingly, Matt Targett will be available at left-back for the trip to West Ham United on Saturday after he missed the win over Villa as he was ineligible to play against his parent club.