The Magpies put in a below-par display against Ronald Koeman’s side, as they fell to yet another defeat.
Newcastle were surprisingly lethargic on the south coast, and it wasn’t until they went 3-0 down that they finally started to show some fight.
The half-hearted performance was highly disappointing and it is claimed that Lascelles expressed his frustrations in the dressing room after the match.
The young defender is one of the most inexperienced players in Newcastle’s first-team squad, but he was reportedly not afraid to ask serious questions of his teammates.
Daryl Janmaat also allegedly expressed his annoyance by punching a changing room wall and breaking two of his fingers.
Newcastle are currently in 19th place in the Premier League table, six points adrift of safety with just a few games remaining.