The probability that Republican front-runner Donald Trump will win his party's presidential nomination dropped sharply in the past week while the likelihood of a brokered convention to potentially chose another candidate rose, according to online predictions market PredictIt.

Trump's probability of winning the nomination fell to 44 per cent on Friday from 67 per cent a week ago, according to the website, which is run by Victoria University in Wellington, New Zealand. For Republican rival Ted Cruz, a US Senator from Texas, it rose to 34 per cent from 14 per cent during the same period.

The probability that the Republicans will have a brokered convention to decide the nominee for the Nov. 8 election jumped to 69 per cent from 43 per cent a week ago.

Celebrity businessman Trump is facing pressure to take a more serious approach to his presidential campaign from supporters worried that a string of recent missteps and controversial comments may do lasting damage.

A Cruz win in Tuesday's primary in Wisconsin would make it harder for Trump to reach the 1,237 delegates needed to clinch the nomination before the Republican national convention in July.

If Trump does not win enough delegates, then the party faces the prospect of holding a contested, or brokered, convention in which party leaders try to negotiate nominating a compromise candidate. – Reuters