United States golf legend Tom Watson called on the PGA Tour to provide full details of its merger with the Saudi backers of LIV Golf on Monday, saying the deal had left a slew of unanswered questions.

In an open letter sent to PGA Tour commissioner Jay Monahan, eight-time major champion Watson said the bombshell agreement announced on 6 June had been brokered "without due process."

The 73-year-old former US Ryder Cup captain posed a series of questions to Monahan in the letter while asking whether the merger was driven by financial necessity.

"What does acceptance of this partnership mean to the Tour? What do we get? What do we give up?" Watson asked.

"Why was this deal done in such secrecy and why wasn't even one of the players who sits on the Tour's Policy Board included?"

Under the deal announced earlier this month, the PGA Tour and DP World Tour have joined forces with Saudi Arabia's Public Investment Fund, which has bankrolled the upstart LIV Golf circuit.

Watson acknowledged that the rise of LIV Golf had threatened the PGA Tour's business model, while creating "unprecedented obstacles and battles of both moral and financial consequence."