The Blades, who are looking to add firepower to their attack ahead of their return to the Premier League, moved to 5-1 to sign Southampton forward Austin over the weekend.
And cross-city rivals Wednesday, who were themselves second-favourites to sign the 29-year-old just last week, have drifted from 5-1 to 9-1.
The big favourites remain United’s fellow Premier League newboys Aston Villa, however, who are at evens.
It looks likely that Austin, who’s meteroic rise from English football’s non-league saw him rewarded with an England call-up in 2015, will move on from Southampton after a frustrating spell on the south coast, which has been blighted by injury.
His best season in the top flight came in the colours of Queens Park Rangers in 2014/15, when he scored 18 goals.
The market move-around follows a tweet by Billy Sharp last night that alluded to the possibility that Austin is in talk with the Bramall Lane club.
Noting the colour of Austin’s red, black and white suit in a photo posted yesterday, the Blades icon wrote “Attire on point - the blades”, followed by a laughing emoji.