Republican presidential candidate Donald Trump. Sean Rayford/Getty Images One of Silicon Valley's top venture capitalists has slammed Donald Trump, labelling him a "loser" and a "hustler" with "mediocre" business skills.

Writing in the Financial Times on Thursday, Michael Moritz, the chairman at the venture-capital firm Sequoia and a former member of Google's board of directors, slammed the caustic Republican presidential hopeful in a scathing column titled "To the bright and the rich of Silicon Valley, Trump is a loser."

The 61-year-old investor attacks Trump's business acumen, a subject the New York real-estate magnate and reality-TV star prides himself on and has made a cornerstone of his campaign.

"In Silicon Valley Mr Trump also fails to get more than a passing grade for his business skills because his actual performance, compared to the myth he has assiduously cultivated, is so mediocre," Moritz says, contrasting Trump with tech founders like WhatsApp's Jan Koum and Microsoft's Bill Gates.

Furthermore, Moritz argues, Trump's immigration policies would block future potential entrepreneurs from entering the country:

Silicon Valley winners are people who fashion something from nothing. Many of them are the sort of people Mr Trump wants to keep from entering America and are victims of prejudice and oppression. Jan Koum, the founder of WhatsApp queued with his mother waiting for food stamps when he came to America from Ukraine. Jerry Yang, the co-founder of Yahoo!, could only speak one word of English — "shoe" — when, as a 10-year-old, he came with his mother from Taiwan.

The investor also critically contrasts Trump with New York billionaires including Michael Bloomberg and Stephen Ross, each of whom Moritz says has a far better track record in business.

"Compared with Mr Bloomberg and Mr Ross, Mr Trump seems little more than a hustler who takes from the rich (lenders he has short-changed, partners he has sued) and also takes from the poor (hapless students of Trump University, tenants whom he has allegedly bullied)."

Moritz does not openly back Hillary Clinton, the presumptive Democratic presidential nominee. But he has previously donated to the Democratic Party.

Trump's business credentials and past ventures have come under scrutiny during his candidacy, from the failed Trump Steaks to bankrupt casinos.

Trump University, a real-estate training program, has come up repeatedly during the presidential race, as it is the subject of class-action lawsuits. Trump came under heavy criticism recently after saying the judge overseeing Trump University cases could not do his job because of his Mexican heritage, a statement House Speaker Paul Ryan called "the textbook definition of a racist comment."

Trump has been criticised by many in the American tech industry, with few tech workers backing his campaign and influential investors like Marc Andreessen speaking out against him. Even Mark Zuckerberg, the founder of Facebook, has taken a veiled dig at Trump.

But the presumptive Republican presidential nominee does have a spattering of support in the tech industry. Peter Thiel, a venture capitalist and early Facebook investor who made news recently for secretly funding a legal war against the news site Gawker, is a delegate for Trump.

Trump's campaign has been accused of outright racism by many, promising to ban noncitizen Muslims from entering the US, accusing Mexican immigrants of being rapists, calling for the US military to commit war crimes by targeting the families of terrorists and use torture as an interrogation technique, and laying out a plan to build a huge wall on the country's southern border.