Dutch striker Joshua Zirkzee was the first to arrive on July 14 before defender Leny Yoro joined from Lille four days later.
United then added three more signings in August, as defenders Matthijs de Ligt and Noussair Mazraoui were brought in from Bayern Munich before a deal for former Paris Saint-Germain midfielder Manuel Ugarte was finally completed on deadline day.
INEOS chief executive Sir Jim Ratcliffe - who took control of sporting operations at Old Trafford after securing a minority stake in United in February - had been keen to get business done earlier in the summer.
According to ESPN, Ratcliffe expressed his frustration at a staff meeting shortly before the FA Cup final on May 25 when he bemoaned that United's recruitment operation was not yet 'up to full speed.'
Joshua Zirkzee (left) and Matthijs de Ligt (right) both joined Manchester United this summer
Part of the delay was said to be down to the difficulties United experienced in completing sporting director Dan Ashworth's move from Newcastle.
The report by ESPN claims that multiple agents were left in limbo early in the summer after being told by United: 'We're waiting for feedback from INEOS.'
Signing a new central defender and a striker were United's top priorities.
Before signing Zirkzee, United were also linked with Ivan Toney from Brentford and Lille frontman Jonathan David.
While Toney was ruled to be too expensive, ESPN reports that United were exploring a deal for David - who would have cost up to £25.3million - right up until the moment the Zirkzee deal was finalised.
United paid Bologna £36.5m for Zirkzee, who scored on his Premier League debut in a 1-0 win over Fulham on the opening day of the season.
Canada international David stayed at Lille this summer despite the external interest in him.
The 24-year-old has scored 87 goals in 189 appearances for the French club.