Many activities can trigger a groin injury: being told you are dropped is not among them. Robert's reaction was more knee-jerk than hernia-inducing.
The Frenchman claims he did not refuse to sit on the bench, but merely wanted to rest. So why wait until the team is revealed to inform the manager of an injury you claim to have been nursing for 48 hours?
"I'll be asking Laurent some questions on Monday," revealed the manager, Alain Perrin, who bought some valuable breathing space thanks to a stunning comeback courtesy of four goals in 26 second-half minutes to secure a second League victory this season.
"I'm told he says he was injured in training on Thursday, but he trained as normal on Friday. He should have told me he was injured before I named the side. He could have stayed at home and I'd have brought someone else."
Robert's self-centred approach is the last thing needed by a multi-national squad working hard on engendering a little team spirit. "If players don't want to fight it's better for them to say so and they don't have to play," Dejan Stefanovic, the defender said.
Matthew Taylor inspired only a fifth Premiership victory of the calendar year, to ensure Robert has plenty of recovery time, as Perrin will be loath to tinker with this winning side.
The second of the midfielder's two goals, a 40-yard driven lob, is already a contender for goal of the season. Taylor was involved in all his sides' goals, flicking on for Zvonimir Vukic to drill the equaliser, before pouncing on a comical mix-up between Kelvin Davis and Alan Stubbs to put Portsmouth ahead.
Dario Silva headed in Taylor's perfect cross to complete the rout and cue a mass exodus of Sunderland fans, who had seen their side equal Nottingham Forest's record of 16 Premiership games without a home win.
Those who remained taunted Davis, who, despite failing to convince, has harshly been cast as scapegoat for a rapidly disintegrating season. On current form, Sunderland will easily dip under the Premiership low of 19 points they were relegated with in 2003.
"If the fans want to blame Kelvin for Taylor's second, they might as well blame him for every natural disaster there's ever been in the world," said McCarthy, in defence of his goalkeeper.
Dean Whitehead's fourth-minute penalty - following a handball by Brian Priske - had given Sunderland the lead, making their second-half capitulation even more unfathomable.
McCarthy was tempted to join the exodus, and left his players in little doubt as to his feelings: "We were piss poor and I can understand fans leaving early. I've told the players it was an embarrassment." Not as big an embarrassment as Laurent Robert.
Goals: Whitehead (4) 1-0; Vukic (48) 1-1; Taylor (59) 1-2; (67) 1-3; Silva (74) 1-4.
Sunderland (4-4-2): Davis; Nosworthy, Stubbs, Caldwell, Hoyte; Lawrence (Stead, 62), Whitehead, Miller (Robinson, 50), Welsh; Elliott, Gray. Substitutes not used: Alnwick (gk), Woods, Murphy.
Portsmouth (4-5-1): Ashdown; Griffin, Primus, Stefanovic, Priske; Taylor (Todorov, 84), Hughes, Vukic (Viafara, 68), O'Neil, Vignal; Silva (Mbesuma, 78). Substitute not used: Westerveld (gk).
Booked: Portsmouth Griffin.
Referee: M Halsey (Lancashire).
Man of the match: Taylor.
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