The former England and Twente boss has hailed the midfielder, who saw a proposed move to Everton collapse during the January transfer window after failing a medical
The Dutch midfielder saw a proposed January move to Merseyside collapse due to issues with his medical, after the clubs had agreed a €10 million fee.
And McClaren, who was still in charge of Twente at that time, claims that Fer's failed switch largely contributed to his sacking a month later.
He told Yahoo! Sport: "I think one of the main reasons Twente and I were on a little bit of a dip in February, and resulted in me leaving, was because we were selling one of the players who I thought was perfect for the Premier League, Leroy Fer.
"That fell through for medical reasons and it was a hindrance to us because he was very disappointed not to get the move and that had a big impact on our team.
"We also had a centre-half called Douglas, who many Premier League teams have been chasing for a long time. Nacer Chadli also.
"There are good players in Holland who are technically and tactically gifted that are knowledgeable about the game, they could adapt to English football."
McClaren endured an unsuccessful 18 months in charge of England between 2006 and 2007, losing his job after failing to guide the Three Lions to Euro 2008.
However, the York-born boss believes he has improved since then having managed in the Bundesliga and Eredivisie, and suggests English football can learn a lot from the "technical and tactical" aspects of the game abroad.
"One of the key things I took from Holland was how to develop young players," he continued.
"English players are well known for their physicality and mentality but I think we need to add that technical and tactical aspect if we are to develop our game as well.
"What I know now compared to what I knew five years ago is incredible. The experience and knowledge I have gained, moving to another country and having to adapt to another culture.
"The English culture is all about results, winning and losing is the be-all and end-all. Whereas the focus in Holland is more on the technical, tactical and possession aspects of the game – playing beautiful football.
"It’s all about bringing young players through and not so much results. They do, however, still want results and we married that concept for the first two years very well at Twente. When people ask me if I would recommend playing or coaching abroad I always say definitely because you really grow."
The 51-year-old also insisted that the results-driven nature of modern football means short-termism among chairmen is something managers must live with.
"Managers know that if they don’t deliverer what the chairman and owner wants they are in danger of losing their job," he added. "That’s part of the game, that’s football and we accept it.
"For example, I was at Middlesbrough for five years but then only in Germany for nine months. It doesn’t make you a bad manager or a bad owner, it just means that the fit is wrong.
"Everything is about results and about winning. The majority of business people coming into football are successful, so when they take over a football club they automatically expect it to be successful, but there also needs to be someone with football knowledge and it’s about marrying those two together for the common good of the club."
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