Tim Sherwood has been appointed director of football at struggling League One club Swindon Town, reports BBC Sport.
Swindon head coach Luke Williams, who signed a five-year deal in March, will remain in his role at the club, who are in the relegation zone after 16 games.
"This is one of the biggest appointments the club has ever made," chairman Lee Power told BBC Wiltshire.
"We're still a bit shocked that we've managed to persuade Tim to take it on.
"We're very mindful not to use the title 'manager' - it's not a demotion for Luke Williams. He'll be head coach still. Tim will be running training alongside (Luke)."
Sherwood added: "I like this club. I've got a soft spot for it. This is a good opportunity for me to get back onto the training field.
"I started this morning. I'll be in the dressing room; I'll be talking to the boys and giving them some words of wisdom."
Power said that Sherwood will "head up all aspects, including transfers, the way we play, the formations and the picking of the team", implying a strong level of day-to-day involvement.
"A director of football is normally someone who doesn't put their tracksuit on and doesn't interact with the team - that won't happen here," said Power.
"Luke (Williams) is thought of in the football world as a top, top coach - that will continue.
"Something needed to change and happen. This season, it hasn't been good enough."
Power continued: "Everyone knows Tim has been a friend of mine for 25 years. So there won't be a contract.
"It's a special relationship that we've had for a very long time - he definitely isn't coming for the money.
"Tim has had opportunities to work for two Championship clubs this year that he has turned down."