Moussa Dembele has sealed his six-month loan move to Atletico Madrid, with Islam Slimani arriving at Lyon to take his place.
Dembele arrives at the LaLiga champions as a direct replacement for Diego Costa, who left the Spanish giants last month, with a reported £29.6million option to buy in the summer.
The 24-year-old enjoyed two prolific seasons in front of goal in France after arriving from Celtic in 2018.
He leaves after notching 45 times in 108 appearances, including a brace in last season's Champions League quarter-final victory over Manchester City.
Algerian international Slimani has in turn ended his miserable spell at Leicester by signing an 18-month deal at the Ligue 1 leaders.
Slimani made the last of just 48 appearances in four-and-a-half years at the Foxes in a 1-0 defeat by Aston Villa last October.
The 32-year-old was a £28m signing in August 2016 but never truly settled, and has been sent out on loan in each of the last three seasons.
Atletico boss Diego Simeone confirmed this week that the club were closing in on the signing of Lyon forward Dembele.
The need for a replacement for Costa had been sharpened when he cancelled his contract at the club six months early in December.
'It's still not confirmed, but it's very advanced,' the Atletico coach told reporters.
'I'm going to turn my head towards the game, which is what interests me, and when there's something [on Dembele], if there is something, I'll give an opinion.'
Simeone's comments come after Lyon sporting director Juninho revealed the striker had come to speak to him about his desire to leave.
'Moussa came to see me. He thinks that this is the moment to change teams, that he has lost a bit of motivation,' the Brazilian said.
'This was not something we foresaw. I like him a lot. Keeping someone who does not really want to keep up the intensity through the next five months - that is not ideal.
'We are in talks with Atletico, I think that Moussa has found an agreement with Atletico.'
Dembele has scored just one Ligue 1 goal this season from 16 top-flight appearances in France, after a season in which he hit 24 in 46 across all competitions.