Social Democratic Party (SPD) leader Martin Schulz addresses a news conference in Berlin, Germany, May 15, 2017. REUTERS/Hannibal Hanschke

BERLIN (Reuters) - The approval rating of Martin Schulz, Germany’s top Social Democrat, slumped to its lowest level in a poll conducted by Infratest dimap since the former European Parliament president was named as the party’s chancellor candidate in January.

Schulz’s rating dropped six percentage points to 36 percent over the past month, the poll showed.

Schulz and the center-left Social Democrats (SPD) had hoped to unseat Chancellor Angela Merkel, who is seeking a fourth term in Sept. 24 national elections, but the party has lost momentum after initial gains seen after Schulz took over the party’s leadership in January.

Merkel’s approval rating rose one percentage point to 64 percent in the latest poll, her best showing since August 2015, shortly before she opened the doors to over a million refugees mostly from the Middle East, the pollsters said.

In a direct election, 53 percent of Germans said they would vote for Merkel, up four percent from last month, while support for Schulz dropped seven percent to 29 percent, according to the poll of 1,503 eligible voters taken June 7 and 8.

The center-left SPD, junior party in Merkel’s current right-left coalition, had hoped to form a government on its own with smaller parties.

The poll showed Merkel’s conservative Christian Democrats winning 38 percent of the vote, a gain of one percent from early May, while the Social Democrats dropped three percentage points to 24 percent.

The pro-business Free Democrats gained two percentage points to 10 percent, while the pro-environment Greens dropped one percentage point to 7 percent, the Left party gained one point to eight percent and the anti-immigrant Alternative for Germany (AfD) dropped one point to 9 percent.