The 32-year-old former Argentina international has been pinpointed following Vincent Kompany's groin injury, while the Manchester City coach also hopes Gareth Barry will stay
Goal revealed on Tuesday that the Premier League runners-up had agreed a deal in principle for the transfer of the centre-back worth up to €4.7 million.
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"I expect progress," Pellegrini told reporters. "I hope that we can get one more defender for the team.
"Maybe he’s the name we want. We will see what will happen with him."
Pellegrini also insisted Gareth Barry remains part of his plans, despite rumours of a move to Everton for the midfielder.
The 59-year-old wants the England man to stay and fight for his place at the Etihad Stadium, and hopes he will provide competition to the likes of Yaya Toure and Fernandinho, despite failing to feature so far this season.
He explained: "All the players have a future here. At the moment we have all of the squad fit.
"We have 23 players it’s impossible for all of them to be playing.
"Gareth Barry is an important player but we also have Toure, Fernandinho, [Jack] Rodwell and Javi Garcia, so we have four players in that position."