Monaco have announced the signing of Chile international defender Guillermo Maripan on a five-year deal from Alaves.
The fee is said to be €18 million (£16m/$20m).
Monaco have endured a difficult start to the season in Ligue 1 after being in relegation difficulty throughout 2018-19.
They have gone down to consecutive 3-0 defeats to start this campaign, and have seen a player dismissed in each game.
The club welcomed the signing of the 23-cap international, who moved to Spain from his native Chile in 2016.
“We are very pleased to welcome Guillermo to AS Monaco,” Oleg Petrov, the French club’s vice president, said in a statement.
“He is an athletic defender with personality, who has demonstrated his potential in the Spanish league, and also with the Chilean national team.
“I am convinced that Guillermo will find everything he needs to continue to progress and do very good things with AS Monaco.”
Maripan turned out 47 times for Alaves over the last two seasons, which have seen them finish 14th and 11th.
He played all 90 minutes at centre-half in their opening La Liga game this year, helping his team keep a clean sheet in a 1-0 victory over Levante.
He said he was excited to join Monaco who have struggled to regain the form that saw them win Ligue 1 and reach the Champions League semi-finals in 2017.
“It’s an honour for me to join AS Monaco, one of the biggest winners in French football,” the 25-year-old said.
“It’s an ambitious club with great players. I look forward to stepping on the field and being able to demonstrate my qualities.”
Monaco have already played two different pairings at the heart of the defence this year.
Highly-rated England Under-19 international Jonathan Panzo started their first game alongside Kamil Glik, but was relegated to the bench for the second match of the year.
Glik retained his place, with another teen starting alongside him. Benoit Badiashele, like Panzo, is just 18, but his inclusion saw no change in the outcome as Metz put three past the new-look pair.