This has been verified by Marouane Fellaini, who produced arguably his best performance since arriving at Old Trafford in the summer of 2013 during the 3-0 win over Spurs, as well as Van Gaal himself.
Fellaini briefly mentioned what Rooney said during the meeting - it centred around qualifying for next season's Champions League campaign - and judging by the performance and United's excellent performance it seemed to have the desired effect.
"I think last night the captain talked to the team about next season for the Champions League," Fellaini told BBC Sport, according to the Manchester Evening News. "I think it affected the team and I think it was an important speech."
Van Gaal, despite not being involved in the meeting, was delighted Rooney had taken it upon himself to motivate his teammates.
Van Gaal: I was not involved in meeting
"I was aware but I was not involved. It was the captain who was involved," the veteran Dutch coach was quoted as saying by Goal.com. "The players knew that this game was massively important and so I think the captain has to do something to help the players or the manager or the club. I was very pleased."
Fellaini scored the game's opening goal with a sweet left-foot finish, while Michael Carrick and Rooney added two more before half-time.
United still have plenty to prove over coming weeks
In what was undoubtedly Manchester United's best performance so far under Van Gaal, supporters will be hoping this display was more than an anomaly.
The Red Devils are currently five points clear of Liverpool in fourth place - although Brendan Rodgers' side can reduce the gap back to two points when they take on Swansea City this evening - and remain on course to qualify for the Champions League with nine matches remaining.
United have managed to come through their first test with little trouble, but a daunting few weeks kicks off this weekend with an away trip to Liverpool.
Following their match against Aston Villa a week later, Van Gaal's men go head-to-head with Manchester City, Chelsea and Everton in April before facing Arsenal in May.
But after Sunday's comprehensive win over Spurs, Van Gaal will be looking to the likes of Fellaini and Rooney to produce similarly talismanic performances in order to ensure United secure Champions League football for next season.
Manchester United fans: after Sunday's 3-0 win over Spurs, are you confident your side will secure a top-four finish? Let us know by leaving a comment in the box below!