May's Brexit deal suffered a crushing defeat in parliament on Tuesday, raising the prospect of the government seeking a different plan or leaving the EU with no deal at all.
"Theresa May could sort this out now if she had a real discussion, a real approach to compromise, bring all the parties together," John McDonnell told BBC radio.
"I think there could be a compromise, most probably on the basis on what Labour's advocating. But the problem that she's got is I just don't believe people have any faith in her any more to be able to deliver that." (Reporting By Andrew MacAskill and James Davey Editing by William Schomberg)