Lo Celso, 20, has joined the Ligue 1 champions from Rosario Central on a five-year contract but will remain on loan with the Argentine club.
Genoa have signed Giovanni Simeone, the son of Atletico Madrid head coach Diego Simeone, from River Plate.
Sevilla completed the signing of Argentina defender Gabriel Mercado from River Plate on Thursday.
Argentina forward Carlos Tevez revealed that new Chelsea boss Antonio Conte tried to convince him to join the London club.
Paris Saint-Germain have completed the long-awaited signing of Giovani Lo Celso from Argentine club Rosario Central on a five-year deal.
Atletico Madrid are to sign goalkeeper Axel Werner this summer according to the Argentina under-23 international's current club, Atletico Rafaela.