LONDON (AP) — The U.S. ambassador to Britain has cast doubts on whether a major bilateral trade deal can be reached if Parliament approves the Brexit proposal from Prime Minister Theresa May.

Robert "Woody" Johnson told BBC radio Monday that negotiating a "quick" and "massive" trade deal between the two longtime allies "doesn't look like it would be possible" under the terms of May's proposed deal with the European Union.

Johnson used a live radio appearance to reiterate President Donald Trump's concerns about the proposed agreement, which faces strong opposition in Britain's Parliament.

May has said she plans to bring the plan to a vote in mid-January.

The U.S. ambassador said he finds a "defeatism" in the British attitude toward Brexit that overlooks the many positive developments leaving the EU could bring.