Mikel Merino is set to become the fifth summer signing.
The 21-year-old yesterday underwent a medical ahead of a season-long loan move, with an obligation to buy, from Borussia Dortmund.
United manager Benitez believes Merino has the “quality” to improve his midfield.
“It’s not quite done yet, but we’re working to try and finalise everything,” said Benitez, whose side beat Bradford City 4-0 at Valley Parade last night.
“I’m quite confident that we’ll do it.
“Hopefully, it will get done and we will have a player with quality, who can help us in the middle of the park.”