Brighton and Hove Albion have tabled an offer for Aleksandar Mitrovic.
The Newcastle United striker hasn't played for the club for more than a month because of a back injury.
Mitrovic, 23, returned to training earlier this month, but he wasn't involved in last weekend's 3-1 defeat to Manchester City.
Brighton's offer is understood to fall short of United's £15million valuation.
For his part, Benitez, hopeful of signing a striker in this month's transfer window, will not sell him unless a replacement can be secured.
Mitrovic, signed from Anderlecht in the summer of 2015, has been used sparingly by Benitez over the past 18 months.
And the Serbia international, desperate to be playing week in, week out ahead of the summer's World Cup finals, told the Gazette of his frustration in November.
"I’m patient, but we will see," said Mitrovic. "My patience is almost to the end, so we will see. I want to play. I want to be on the pitch. I’m patient, but we will see.”