The defender joins Barca on-loan from Valencia with the option to buy.
"We are in a delicate moment with our centre-backs and so far we have managed it well, but we don't know how it will go going forward," Valverde explained in a press conference on Friday.
"We took into account the situation of the club and we wanted someone on loan who could play immediately and who knew the league well.
"Murillo met those requirements and he can help us in the short term so the club did a good job with his signing.
"Signings at this club need to be familiar with us as we're continuing our fight for two major competitions soon and we couldn't have brought along players who need to adapt.
"Murillo is a good player who can help us and be important for us so we will push forward and hope for the best."