The hosts have lost eight of their 10 league games so far this season, while the visitors have won seven out of 10 to move four points clear at the summit.
Match preview
After ending their winless start to the season with a surprisingly comfortable 3-0 victory at home against Eintracht Frankfurt, Bochum were thrashed 4-1 away to potential relegation rivals Stuttgart last weekend.
Their opponents had yet to win all season themselves, but goals from Silas and Wataru Endo after the break settled the game as a contest after Simon Zoller had pulled one back before the break.
The defeat leaves Bochum two points adrift at the bottom of the table heading into the weekend. However, Thomas Letsch's side progressed to the third round of the DFB-Pokal in midweek with a 1-0 win away to SV Elversberg, who had stunned Bayer Leverkusen in the first round.
Given that they are four points from safety, even a shock victory against the league leaders would not see Der Blau move out of the automatic relegation places, but it would at least see them climb above Schalke 04 prior to their fellow strugglers facing Hertha Berlin later on Sunday.
Union Berlin have only been in the Bundesliga two seasons longer than Bochum, but after a similar first season saw them finish in 11th place, they have made considerable forward strides since.
After qualifying for the inaugural Europa Conference League with a seventh-placed finish, Urs Fischer's side were only one point away from upgrading to the Champions League last season, but they instead came fifth and are competing in the Europa League as a result.
While their progression to the knockout stages in that competition hangs in the balance after two wins and two defeats from four games, Die Eisernen have stunned German football to move four points clear at the top of the Bundesliga table after 10 matches.
Janik Haberer scored a brace in a 2-0 win against Borussia Dortmund at Stadion An der Alten Forsterei last weekend, with goalkeeper Gregor Kobel's costly error allowing Fischer's side to get off to the perfect start after only eight minutes.
Despite resting several key players, Union Berlin defeated Heidenheim by the same scoreline in the DFB-Pokal in midweek to sustain their three-pronged attack in terms of competitions to compete for, and their raised expectations will mean that anything but a win in Bochum on Sunday would be a huge disappointment.
VfL Bochum Bundesliga form:
L
L
D
L
W
L
VfL Bochum form (all competitions):
L
D
L
W
L
W
Union Berlin Bundesliga form:
D
W
W
L
W
W
Union Berlin form (all competitions):
L
W
W
W
W
W
Team News
Bochum could be without Michael Esser, Paul Grave, Konstantinos Stafylidis, Takuma Asano, Jacek Goralski and Lys Mousset at the weekend due to injury.
Letsch only made one change for the cup win against Elversberg on Wednesday, with the rested Zoller likely to return to the starting XI having scored in his side's defeat to Stuttgart last weekend.
Perhaps unsurprisingly given their involvement in Europe, Fischer made five changes for his side's victory against Heidenheim, with Jordan Siebatcheu expected to return alongside Sheraldo Becker in attack.
Kevin Mohwald is likely to miss out once again as he continues to return to full fitness after a muscle strain.
VfL Bochum possible starting lineup:
Riemann; Gamboa, Ordets, Heintz, Soares; Losilla, Stoger; Zoller, Forster, Holtmann; Hofmann
Union Berlin possible starting lineup:
Ronnow; Jaeckel, Knoche, Leite; Ryerson, Haraguchi, Khedira, Haberer, Giesselmann; Becker, Jordan
We say: VfL Bochum 0-2 Union Berlin
We expect a comfortable win for the visitors, who rarely give up leads when they edge ahead in matches.
Indeed, Union Berlin have won five matches in a row without conceding in all competitions, so Bochum have a serious job on their hands to even score against Fischer's table toppers.