The 22-year-old scored two goals for Newcastel’s reserves at Wigan on Monday, but broke his toe in the game.
“Xisco’s expected to be out for three weeks, and it’s a real blow,” Newcastle coach Chris Hughton told the club’s official website.
“He’s got a toe injury. At the time he did it, he tried to carry on, but he was struggling. It’s very, very swollen, and it’s looking like a few weeks.
“The game on Monday was an ideal time to play some players. Alan Smith, of course, came through fine, and Cacapa got 90 minutes.
“They’re all pluses, but unfortunately, 10 minutes before the end, Xisco suffered his injury. If he hadn’t, it would have been a good exercise.”