Leicester defender Caglar Soyuncu has "agreed a four-year deal" with La Liga side Atletico Madrid, a source close to the player has told BBC Sport.
Soyuncu, 27, is out of contract this summer and will be the second player to leave on a free after Youri Tielemans.
The Foxes finished 18th in the Premier League this season and were relegated to the Championship.
Atletico boss Diego Simeone appeared to confirm the signing in an interview with Spanish radio on Thursday.
The Argentine told Cope:
"Atletico is going to sign what they can sign. We know what we need. Soyuncu is already signed and is going to help us."
Turkey international Soyuncu joined Leicester from German side Freiburg for £19m in 2018 and has played 132 games for the club, winning the FA Cup and Community Shield in 2021.
He was frozen out by former manager Brendan Rodgers for much of this season, playing only two league games, but interim boss Dean Smith restored him to the side immediately after taking over.
Although he featured five times since April, he missed the last three games of the campaign because of a hamstring injury.
"An agreement in principle was made in January," said the source. "Caglar decided he didn't want to prolong his contract with Leicester.
"For a long time we have been in contact with [Atletico Madrid sporting director] Andrea Berta. He kept checking to see if he wanted to leave England.
"Atletico were interested in signing him a year ago but Leicester did not want to let him leave and so they waited on him."
Soyuncu featured in both of Turkey's European Championship qualifying fixtures in March and should link up with for the national team's games against Latvia and Wales later this month, after which his signing is officially expected to confirmed.
Leicester are not likely to make Brazilian winger Tete's deal permanent, while Jonny Evans, Nampalys Mendy, Daniel Amartey and Ryan Bertrand all out of contract this summer.