Newcastle United faced a 4-0 defeat against Celtic in their first pre-season friendly, with Alexander Isak absent from the squad. The 25-year-old Swedish striker's future remains uncertain amid transfer speculations this summer.
The absence of Isak, along with Joelinton, was felt as Eddie Howe's team struggled against the Scottish champions. Celtic took the lead in the 28th minute when Arne Engels converted a penalty after being fouled by Joe Willock inside the box, sending goalkeeper Nick Pope the wrong way.
Just before half-time, Pope made a critical error by rushing off his line and failing to clear a long ball, allowing Johnny Kenny to score into an empty net, doubling Celtic's advantage.
Newcastle introduced Anthony Elanga, a recent £55 million signing from Nottingham Forest, at the break. However, the winger was unable to make an impact at Celtic Park.
Celtic extended their lead seven minutes into the second half when South Korean Yang Hyun-Jun scored past substitute goalkeeper Martin Dubravka from close range. Despite Newcastle's increased possession in the second half, they conceded a fourth goal when Liam Scales headed into the top corner in the 75th minute.
Newcastle will face Arsenal in their next pre-season match on Sunday, 27 July, in Singapore, with kick-off at 12:30 BST.