Defender Malang Sarr has joined Chelsea on a free transfer.
The 21-year-old left Ligue 1 club Nice this summer and has now signed a five-year deal at Stamford Bridge.
The highly-rated centre-back will now head out on loan, with the Blues hopeful of a fruitful long-term future in west London.
Nice-born defender Sarr racked up more than 100 appearances at his hometown club since his senior debut aged just 17.
"The opportunity to sign Malang was one we could not miss," said Chelsea director Marina Granovskaia.
"He is a tremendous prospect and we will be monitoring him closely during his loan period, hoping he will soon be back at Chelsea.
"We are very happy to welcome him to the club today."
Arsenal head coach Mikel Arteta says captain Pierre-Emerick Aubameyang is yet to sign his new contract with the club.
It was expected an announcement would have been made over the last fortnight that the 31-year-old, who scored both goals in the 2-1 FA Cup final win over Chelsea, had agreed fresh terms at the Emirates Stadium.
But, with just one year remaining on his current deal, Arteta says nothing is yet set in stone.
"Well, I keep being positive," he said when asked if he had any news on Aubameyang's contract.
"We have some really good talks with him and his agent and I am pretty confident we will find an agreement soon. That's my feeling."
Lazio have signed goalkeeper Pepe Reina on a permanent deal from Serie A rivals AC Milan.
The 37-year-old spent the second half of last season on loan at Aston Villa, whom he helped secure their Premier League status.
An AC Milan statement on their official website read: "AC Milan announces that Jose Manuel Reina Paez has joined SS Lazio on a permanent deal.
"The club wishes the footballer all the best for the next sporting seasons."
Welcome to #CelticFC, @10DavidTurnbull! 🍀⚪️
— Celtic Football Club (@CelticFC) August 27, 2020
Celtic have completed the signing of David Turnbull from Motherwell.
The 21-year-old midfielder almost joined Celtic in June 2019 in a £3m transfer – which could have risen to £3.25m – only for a latent knee problem to emerge in the medical.
After proving his form and fitness in recent weeks following surgery, Turnbull sparked another bid from Celtic which has been accepted.
Motherwell said the fee was nearly double their previous transfer record – which was the £1.75m received from Celtic for Phil O'Donnell in 1994.
Meanwhile the Premier League's record appearance holder Gareth Barry has announced his retirement from football at the age of 39.
Barry, who played 653 times in the top flight, represented Aston Villa, Manchester City, Everton and West Brom during a career spanning four decades.
The midfielder scored 53 goals and produced 64 assists in the Premier League and won 53 caps for England between 2000 and 2012, scoring three goals for his country.
He played his final game in March this year when he started West Brom's 3-2 FA Cup defeat to Newcastle at The Hawthorns.
