Fellaini joined United from Everton, Moyes's former club, in a 27.5 million pounds move on transfer deadline day.
Manchester United great Ryan Giggs has described former manager David Moyes's decision to buy Marouane Fellaini from Everton in September 2013 as a "panic" buy.
Fellaini joined United from Everton, Moyes's former club, in a 27.5 million pounds ($33.6 million, 30.9 million euros) move on transfer deadline day.
But the gangly Belgium midfielder became a symbol of United's struggles under Moyes, who was sacked in April 2014 after just 10 months in the job.
"I don't blame David," Giggs wrote in Saturday's Daily Telegraph. "United had signed players late in the window before. This time was different. It was more of a panic."
Giggs stepped in as caretaker manager following Moyes's departure and steered the club to a seventh-place finish in the Premier League.
Giggs said Moyes, now the Sunderland manager, spent his entire United tenure playing catch-up following his appointment as the successor to Alex Ferguson.
"He came in without any of the inside knowledge about how the squad worked: when certain players needed resting, who was right for which game, who needed to be moved on and who needed to be encouraged," Giggs said.
"Sir Alex (Ferguson) might not necessarily have had a first-choice XI, but he knew exactly what side was needed for each game and would have that planned weeks ahead.
"David did not have that information. He started with a blank sheet of paper and for most of the first season we were chasing our best XI, or the right team for the game in question."
United finished fourth and fifth under Moyes's successor, Louis van Gaal, before Jose Mourinho was appointed manager last May.
Giggs, who made a club-record 963 United appearances, worked as Van Gaal's assistant, but left after the arrival of Mourinho.