The Premier League champions are set to launch an internal inquest after David Moyes and new chief executive Ed Woodward missed out on a number of high-profile targets, and only landed Marouane Fellaini late on deadline day for an inflated £27.5 million fee.
Comolli believes the loss of Sir Alex Ferguson and David Gill in the same summer has had a huge impact at Old Trafford, and says the club have paid a high price for a lack of forward planning.
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"If there was a club in need of a director of football to ease the process for both individuals [Moyes and Woodward] it was Manchester United.
"David [Moyes] only joined on July 1 which was quite late. For some reason the club weren't prepared or they didn't think it would be that difficult and they ended up in a difficult situation."
United only managed to bring in Guillermo Varela from Atletico Penarol and Fellaini, and missed out on a host of targets including Thiago, Cesc Fagregas, Ander Herrera, Fabio Coentrao and Sami Khedira.
Comelli signed Gareth Bale, Luka Modric and Dimitar Berbatov while at Tottenham, but was also behind Liverpool's underwhelming 2011 transfer season when they lavishly spent on Craig Bellamy, Jordan Henderson, Stewart Downing and Sebastian Coates, as well as the flop signing of Andy Carroll the period before.