Lazio have competed the signing of Angola international defender Bastos from Russian Premier League side Rostov.
The 24-year-old played in both legs of Rostov's Champions League qualifying victory over Anderlecht - the club's European debut - but was not part of the matchday squad for Tuesday's 1-1 draw at Ajax as his move to Lazio neared completion.
"SS Lazio announces the acquisition of the registration of the player Bartolomeu Jacinto Quissanga, coming from Russian club FK Rostov," read a statement on Lazio's official website.
The terms of the transfer were not disclosed, although Lazio are reported to have sanctioned a fee in the region of EUR6.5million.
Bastos made 84 appearances for Rostov after joining from Petroleos Luanda in his homeland in July 2013, scoring four times.
He joins Moritz Leitner, Jordan Lukaku, Ciro Immobile and Wallace among the new arrivals at Lazio, who begin their Serie A campaign at Atalanta on Sunday.