A survey by research group Forsa found that the far-right Alternative for Germany party (AfD) had sunk to eight percent in support, down from a high of 13 percent in March, while other polls had recorded 15 percent support as recently as May.
Party leaders had praised the Brexit vote when results were announced, with MEP Beatrix von Storch saying she had "cried with joy".
Recently the party has made a number of blunders that may be putting voters off, including casting racist insults at members of the national football team during the European Championship, and splitting apart over anti-Semitic comments made by one of its politicians.
The AfD began as a Eurosceptic party in 2013, but it has more recently taken on increasingly far-right views.
The party had ridden a wave of success through state parliament elections earlier in the year on the back of criticism of Germany's acceptance of numerous refugees, securing more than 24 percent of the vote in Saxony-Anhalt.
But with the number of new asylum seekers dropping in recent months, the party's anti-immigrant rhetoric is perhaps losing some of its resonance.
The new Forsa poll published by Stern Magazine and broadcaster RTL on Wednesday shows how these events have impacted the party's level of popularity, with numbers dropping each day since the party's own infighting came to a head last week.
AfD co-leader Jörg Meuthen walked out of a party parliamentary group in Baden-Württemberg last Tuesday with 12 colleagues after members failed to vote to oust a colleague who was accused of making anti-Semitic remarks.
“On Monday and Tuesday of last week, nine percent still wanted to vote for AfD,” said Forsa leader Manfred Güllner. “On Wednesday and Thursday - after the division in the Baden-Württemberg state faction - only eight percent and on Friday only seven percent.”
Forsa had polled people between July 4th and 8th.
Of all respondents surveyed, 61 percent said they were doubtful that the party would have a future given all the infighting - but just 14 percent of AfD supporters said the same.
Still, another 29 percent of all polled said they did not believe the AfD would sink into insignificance, while 81 percent of AfD supporters did not think their party would disappear off the political map.
A separate poll last week by newspaper Die Welt and broadcaster ARD also showed that the AfD was the only party to lose support, dropping three points to 12 percent, and that this was because of the Brexit vote.
Research group Infratest Dimap, which conducted the survey, explained that the Brexit vote was most likely behind this drop.
“This is likely the result of the ongoing debate on Europe, in which the EU-skeptical AfD loses support,” Infratest Dimap wrote.
Political scientist Hans Vorlaender of Dresden's Technical University also told Reuters regarding the Forsa survey that the EU referendum results had had a negative impact on the AfD's support level.
"All of a sudden, the populists aren't looking as attractive anymore," Vorlaender said.
Meanwhile Chancellor Angela Merkel's conservative CDU (Christian Democratic Union) and CSU sister party (Christian Social Union) received only a slight bump of one percent to reach 36 percent of respondents' support.
The Social Democrats (SPD) gained two points on the week before to 23 percent while the Green Party was at 12 percent and the Left party had nine percent.