As reported in The Scotsman on Tuesday, it appears that Gullane has been given the nod ahead of near neighbour The Renaissance Club in a search for the 2015 venue.
The news could be announced this weekend and Mickelson appears to have been told of the decision.
“I think this is a great test of links golf and a great way to get ready for The Open,” said the 44-year-old after launching the defence of his title at Royal Aberdeen with a three-under-par 68. “So was Castle Stuart (venue for the past three stagings, as will Gullane).
“It’s great for someone like me to have the opportunity to play these great courses.”
It will mean an emotional return to East Lothian for Mickelson after his first Open Championship success at Muirfield last summer.
Since The Scotsman broke the news, it has emerged that the opening hole on a composite course at Gullane will be the second on the No 1 Course. Three holes on the No 2 Course – the fourth, fifth and 16th – will be used, with the 18th on No 1 being extended by close to 100 yards to make it sterner.
Mickelson, meanwhile, was pleased with an opening effort in Aberdeen that contained a magical wedge shot from a cart path to set up a birdie at the 13th. Earlier, his ball had moved at the tenth but it was caused by the wind and he escaped a penalty due to the fact he hadn’t addressed it.
“I fought hard and it was a really good day,” he said.