With the Blades in need of bolstering their midfield options, reports emerged earlier in the week claiming they were looking to snap up the Netherlands international on a free transfer.
However, Feyenoord have now confirmed on their official website that they've recaptured their former starlet, following a period in which he's trained and played friendlies with the club.
Discussing his move, Fer said: “My heart is here. I'm very happy to be back. I feel stronger and fitter, and I will do everything in my power to get back to my old level as soon as possible, in order to have a great season with Feyenoord."
The news is unlikely to come as too much of a blow to Blades fans, given that the player's reputation for picking up injuries would have made him a risky acquisition. Furthermore, United are understood to be moving closer to signing Nottingham Forest's Ben Osborn, who can play in midfield, among other other areas.
The Blades are also believed to be on the verge of completing a fresh loan deal for Manchester United goalkeeper Dean Henderson, while striker Oli McBurnie remains a key target for Chris Wilder.