Alnwick replaced the injured Rob Elliot at the break against Chelsea on Saturday and became an immediate Geordie hero.
The former Charlton goalkeeper had suffered a recurrence of a thigh injury and will undergo a scan next week.
The castle that Jak built
21-year-old Alnwick was kept busy in a dramatic second half, making a fabulous save from Diego Costa.
Jak Alnwick (told BT Sport): “It’s easier coming on at half-time – you don’t have to think about it.
“It was a great experience. I’m happy to play my first game and get a win for the team.”
The stopper’s only previous first team experience in a competitive game had been for Gateshead in the Conference.
Newcastle actuially signed Alnwick from the Mackems back in 2008 when he was only 15.
The youngster is the younger brother of Ben Alnwick, who is currently playing for Peterborough United.
Jak has played for England at Under-18 level and been in squads for Under-20.
His Wikipedia page was recently hacked and he was credited with “superhuman powers” and building his own castle to celebrate a clean sheet when he kept a shut-out against Blyth Spartans for Gateshead in the FA Cup first round.