Dortmund remain two points adrift at the foot of the table after crashing to a 1-0 defeat at home to 10-man Augsburg on Wednesday.
Hummels and vice-captain Roman Weidenfeller spoke to frustrated supporters post-match following a fifth league match without success.
No one could have predicted Dortmund's demise, having seen Jurgen Klopp's men finish in the top two in the past four Bundesliga campaigns.
However, the danger of being relegated to Germany's second tier for the first time since 1971-72 is becoming an increasing concern.
And Hummels has urged Dortmund to dig deep to avoid the drop, starting against Freiburg, who are only two points above the former.
"We're always chasing games after going behind," Hummels said after Wednesday's defeat. "What's missing is us taking the lead so that we can then sit back and play on the counter.
"We're all aware we've got to fight in these next 15 games.
"Playing attractive football will just be a bonus - we're still expected to play great football.
"Ninety-eight per cent of this is about the fight. The other two needs to be about loosening up so that we start making the right decisions in the final third."
Looking further up the table, league leaders and reigning champions Bayern Munich travel to third-bottom Stuttgart on Saturday in a rare run of poor form.
Since the mid-season break, Bayern have failed to win a match - beaten 4-1 by second-placed Wolfsburg before drawing 1-1 at home to Schalke on Tuesday.
Bayern remain eight points clear at the summit but cannot afford another slip up with Wolfsburg looming large.
Wolfsburg are also in action on Saturday against Hoffenheim and star recruit Andre Schurrle could make his bow for the club following his move away from Chelsea.
Only two points separate Borussia Monchengladbach, Augsburg, Bayer Leverkusen and Schalke ahead of this weekend's fixtures.
Gladbach occupy third position with 33 points, two clear of sixth-placed Schalke, leading into Friday's showdown at Veltins-Arena in Gelsenkirchen.
Augsburg - level on points with Gladbach - host Eintracht Frankfurt on Sunday, while Leverkusen (32 points) make the trip to Werder Bremen, who have won three games on the bounce, on the same day.
Elsewhere, youth team coach Pal Dardai will take charge of second-bottom Hertha Berlin as they travel to Mainz after Jos Luhukay was sacked following Wednesday's loss to Leverkusen.
Cologne tackle Paderborn, while Hamburg and Hannover go head-to-head.
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