The 24-year-old, who impressed at the World Cup in Brazil this year, has become Bruce’s principle target after he was forced to admit defeat in the hunt for Blackburn forward Jordan Rhodes.
Hernandez was pictured at Hull’s Cottingham training ground on Wednesday and, ahead of his side’s Europa League second leg against Lokeren on Thursday night, Bruce said the club are working hard to get the deal done.
“We're close to one or two things," said Bruce, "very close to one in particular, which will be another fantastic addition if we can pull it off.
"It's delicate, but if we can pull it off it will be a record for the club. He's a hell of a player, but there's work to be done.
"Until it's really been rubber-stamped, I'm not going to say anything but it would be a huge one for us."
Hull are in need of strike options following the sale of Shane Long, to Southampton earlier this summer, and they had several bids for Rhodes turned down by Blackburn.
Bruce recently brought in Tottenham captain Michael Dawson to strengthen his back-four – his sixth signing of the summer.