Oriol Romeu's season-ending injury has left the European champions short of holding midfielders, with their only other recognised player in that position, John Obi Mikel, on African Nations Cup duty next month.
Chelsea have been linked with the likes of Corinthians' Paulinho, Newcastle's Cheick Tiote and Everton's Marouane Fellaini.
They have also been heavily touted with a move for a striker, most notably Atletico Madrid superstar Radamel Falcao.
Speaking ahead ahead of Thursday's Club World Cup semi-final against Monterrey, interim manager Benitez said: "The club is working and always looking for good players, so we'll see if there are any surprises."
Benitez admitted the seriousness of Romeu's injury, which he suffered in Saturday's Barclays Premier League win at Sunderland, had taken Chelsea by surprise.
"Oriol Romeu was bad news and we weren't expecting something so serious," he said.
"He'll be fine for the future, he's a young player."
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