Reserve team coach Tommy Craig was absent from Newcastle's friendly against Benfield Bay Plastics and it is thought Lee Clark or Terry McDermott could take over.
It was played down as pure "speculation" but the Chronicle believe he has left the club.
Glenn Roeder and number two Kevin Bond were also in the dugout for the 4-3 win and it seems the coaching set-up is being reviewed.
Ironicly, Craig is a current holder of the FIFA Pro-Licence, and he would have lead the team out at Cardiff if Newcastle had reached last season's FA Cup final.
Craig joined Newcastle as a player in 1974 after the Glaswegian enjoyed spells at Aberdeen and Sheffield Wednesday. He also won one Scottish cap in 1976, the same year United got to Wembley in the League Cup final defeat against Man City.
After making over 100 appearances for United and scoring 23 goals, Craig moved to Aston Villa in 1977. He has also coached at Hibs, Celtic and Aberdeen.