Sky sources understand that Chelsea are close to completing the signing of Kurt Zouma from St Etienne.
The 19-year-old defender is expected to seal his switch to Stamford Bridge before being loaned back to the French club for the remainder of the season.
Reports suggest that Zouma will sign a five-year deal after Chelsea agreed a fee in the region of £12.5m, which would make the Blues the biggest spenders in the transfer window so far.
Chelsea have already spent heavily to bring Nemanja Matic and Mohamed Salah to the club and the arrival of Zouma could push their transfer total past £45m.
Zouma attracted interest from a number of clubs, despite being hit with a lengthy ban in November for a reckless tackle that left Sochaux midfielder Thomas Guerbert with a broken leg.
The France youth international was part of the team that won the Under-20 World Cup last year and Chelsea's scouts identified him as an exciting talent.
When asked about Zouma last week, Jose Mourinho said: "As you can see, Chelsea thinks about the future and when we think about the future, we have scouting, we have contacts, we contact clubs, we contact agents, we contact players that we have permission from clubs, which is the case obviously.
"We try to be in control of the situation, but we think we are doing well."