Long-time boss Menezes, who was set to retire at the end of this month, is in hospital receiving treatment for conditions including a stomach ulcer, the company said in a statement.
"Over the weekend, we learned that Ivan's recovery suffered a significant setback due to complications, which followed emergency surgery on the ulcer," Diageo said.
Diageo, the maker of Johnnie Walker whisky, Tanqueray gin and Don Julio tequila, appointed Crew in March to replace Menezes, making the 52 year-old one of only a handful of women to lead a company in Britain's blue-chip FTSE 100 index.
Crew will join the board as an executive director on July 1, Diageo said on Monday.
The former U.S. military intelligence officer, who was appointed operating chief last year, had been president of Diageo North America, its largest market, and Global Supply from 2020.
She takes on the top role as Diageo is trying to cement its dominance in the United States and establish several premium brands, in a post-COVID world.
Shares in the London-listed drinks firm are down about 7% this year.
Menezes, who joined Diageo after its formation through the merger of Guinness and Grand Metropolitan in 1997, grew sales sharply and steered the company through multiple brand acquisitions as well as a major sustainability overhaul.
'Out of respect for Ivan and his family's privacy, we will not be commenting further at this time,' Diageo said.
Commenting on the news, AJ Bell investment director Russ Mould said, “It’s not the succession Diageo was envisaging but Debra Crew starting a month early is unlikely to create the sort of drama seen at Waystar RoyCo for the world’s biggest spirits maker.
“Stepping up to the plate in these circumstances to replace stricken long-time boss Ivan Menezes may even earn Crew some goodwill and allow her to get an early read on the business and how she plans to grow it.
“In his near decade in charge, Menezes delivered an annualised total return of nearly 8%, a decent showing given this period encompasses the pandemic which massively disrupted Diageo’s on-trade sales. Spirits is a decent business to be in as they are cheap to make and typically have strong brand loyalty.
“However, Crew needs to demonstrate she can make a good return from some of the pricey acquisitions of premium spirits by Diageo in recent years."