The Blues had initially wanted Gusto to move to West London in January, but he will remain with the Ligue 1 outfit for the rest of the season.
The France Under-21 international has made 15 starts this season, providing six assists from 54 appearances in total.
Fabrizio Romano claims that the Premier League giants have agreed to pay €30m fee plus add-ons.
Gusto becomes Chelsea’s seven signing of this month following the arrival of Benoit Badiashile, Andrey Santos, Noni Madueke, Mykhaylo Mudryk, Joao Felix and David Datro Fofana.
Chelsea's newest: Malo Gusto! 👋 pic.twitter.com/wIQ3LkNR9p
— Chelsea FC (@ChelseaFC) January 29, 2023