Oscar Garcia has stepped down as Watford head coach because of ill health just 27 days into his tenure and has been replaced by Billy McKinlay.
The 41-year-old Spaniard was discharged from hospital last week after undergoing tests for chest pain.
He was appointed Hornets boss on 2 September, but the only game he took charge of was a 1-0 defeat by Charlton.
Former Scotland and Blackburn midfielder McKinlay, 45, was brought in as first-team coach last week.
"I had mixed emotions. It was Oscar who brought me here. I was 100% shocked," McKinlay told BBC Three Counties Radio.
"I know he has been recovering well and I expected that recovery to continue and he would be back in business as soon as possible. So it's bittersweet almost.
"But when the owner asked me to take over it was a pretty easy decision.
"It's a brave decision from Oscar. He's put the club's interests as a very high priority. I have a lot of respect for that."
Garcia, who leaves with Watford in fourth place in the Championship, said: "I was closely involved with the appointment of Billy McKinlay, because I was aware that I may not be able to return.
"I always wanted an experienced British coach within our set-up, because it's important to have that mix of cultures and experience with this squad.
"I would like to thank Watford's fans for their kindness during my time here at the club. I will be hoping to see you all as a Premier League club next season."
Garcia led Brighton & Hove Albion to the Championship play-offs last season, but quit the club after failing to win promotion to the Premier League.
After a spell in Israel with Maccabi Tel Aviv, the former Barcelona midfielder returned to England to replace Beppe Sannino earlier this month, but spent a week in hospital after being taken ill the day after the Charlton game.
Watford say there is now no concern over Garcia's health, but he requires rest.
Glasgow-born McKinlay has never taken the top job at a club, but has served as first-team coach at Fulham and is currently assistant manager of Northern Ireland, although he has yet to decide whether he will remain in that role.
He played 22 times for Scotland and made more than 400 appearances during his professional career, appearing for Dundee United, Blackburn and Leicester City between 1984 and 2005.
Garcia's assistant coach pairing of Ruben Martinez and Javier Pereira will remain at Vicarage Road and will accompany McKinlay for Tuesday's visit of Brentford.