"His [Trump's] worst ratings are on the environment and relations with Russia," Gallup said, noting that 61 percent of Americans do not like how Trump deals with Russia.
Gallup said Trump's overall approval rating for handling foreign affairs has dropped from 46 percent to 39 percent, but the decline was likely caused by the trade war with China.
The approval rating regarding relations with Russia has not changed since February, Gallup added.
Trump has faced criticism from Democrats and establishment Republicans for his performance at the July summit with Russian President Vladimir Putin in Helsinki. The meeting took place amid the investigation into allegations of Trump-Russia collusion and alleged Russian interference in the 2016 US presidential election.
The US president has frequently characterized the Russia probe by Special Counsel Robert Mueller as a "witch hunt" that has produced no evidence of collusion in well over a year.
Russia has denied all allegations of collusion and meddling in the US election, saying they have been invented to excuse the election loss of a presidential candidate, as well as deflect public attention from actual instances of election fraud, corruption and other pressing issues.