STORY: Johnson says the European Union must make concessions on the rules - known as the Northern Ireland protocol - to win over the province's unionist community loyal to the United Kingdom, and has threatened unilateral action that the EU says could start a trade war.
McDonald, whose party seeks a united Ireland and is now the region's largest after an election this month, said Johnson did not give details of any proposed legislation which would effectively ditch parts of the protocol.
Johnson agreed to the protocol in 2019 to allow Britain to leave the EU's single market and customs union without controls being re-imposed on the border between the Irish Republic and Northern Ireland, a vital part of the 1998 Good Friday peace deal that ended three decades of violence.
But the plan effectively introduced a customs border between Britain and Northern Ireland, incensing many unionists.
The dispute has stymied another part of that peace deal - power-sharing between Sinn Fein and the Democratic Unionist Party it beat in the election. The DUP has blocked power-sharing because of its opposition to the protocol.
Following the meeting, the leader of Northern Ireland's Democratic Unionist Party (DUP), Jeffrey Donaldson, rubbished the idea that Johnson was taking sides between the unionist and nationalist parties.