The Exeter lock suffered a shoulder injury during the English Prem final loss to Northampton on June 20th, and the 23-year-old is now set for surgery instead of facing Fiji, Argentina and world champions South Africa over the next three weekends.
"Daf is having a shoulder operation and will miss the Wales summer internationals while rehabbing," Exeter director of rugby Rob Baxter told the club's website.
"However, he is expected to be fit for around the start of the new Gallagher PREM season."
Meanwhile Wales head coach Steve Tandy announced Tuesday his 33-strong squad for the inaugural Nations Championship, which begins with a Cardiff City Stadium fixture against Fiji on Saturday.
Although this is the southern hemisphere window, Fiji are playing their 'home' fixtures in Europe for financial reasons.
There are two uncapped players in the Wales squad - Exeter back-row Kane James and Ospreys tight-head prop Ben Warren.
"We have selected a squad of 33 players for the Nations Championship to mirror what will be required for the World Cup in 2027," said Tandy.
He added: "We have an exciting opportunity over the next three weeks in a brand-new competition and can’t wait to get our campaign started against Fiji on Saturday."
Wales endured another woeful Six Nations, finishing bottom of the table, although they did end a three-year losing streak in the tournament, spanning 15 matches, with a 31-17 defeat of Italy in Cardiff on March 14th.
"We want to continue building and to be more consistent in our performances across all three games," said Tandy.
Wales great Leigh Halfpenny, meanwhile, has been appointed interim kicking coach.
The 101-times-capped Halfpenny, who retired at the end of last season, was a member of Matt Sherratt's backroom staff for last year's two-Test tour of Japan.
Wales squad for Nations Championship:
Backs (14)
Josh Adams, Sam Costelow, Dan Edwards, Mason Grady, Kieran Hardy, Joe Hawkins, Eddie James, Max Llewellyn, Ellis Mee, Reuben Morgan-Williams, Blair Murray, Louis Rees-Zammit, Ben Thomas, Tomos Williams
Forwards (19)
Adam Beard, James Botham, Rhys Carre, Ben Carter, Ryan Elias, Kane James, Dewi Lake (capt), Dillon Lewis, Evan Lloyd, Alex Mann, Jac Morgan, Taine Plumtree, Tommy Reffell, Nicky Smith, Gareth Thomas, Aaron Wainwright, Sam Wainwright, Ben Warren, Teddy Williams
Coach: Steve Tandy (WAL)