The Tánaiste's public satisfaction rating has fallen by nine points, in the first poll since the Katherine Zappone controversy.
According to a survey by The Sunday Times and Behaviour and Attitudes, it now stands at just 39%.
It's the second-lowest rating of the five main party leaders - with only the Greens' Eamon Ryan lower, on 34%.
Meanwhile, the poll shows Sinn Féin now leads Fine Gael by 10 percentage points.
Mr Varadkar's party has dropped two points to 23%, while Deputy McDonald's is up three, at 33%.
There's been little change elsewhere in the poll, with Fianna Fáil up one point to 21%, and Labour and Greens unchanged at 5% each.