Lanus got their Primera Division title defence off to the perfect start with a 1-0 win over Boca Juniors.
Newell's Old Boys are hopeful they can bring Lionel Messi back to the club after the 2018 World Cup in Russia, when he will have turned 31.
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.