Dragons will also be without lock Levi Douglas for several weeks after he suffered a leg injury in the pre-season win against Scarlets in Llandovery.
The 31-year-old does not need surgery but faces a battle to feature before the break for the November internationals.
“There is a little bit of a fracture in his leg,” said Tiatia. “He doesn’t need an operation but he will be out for a little while.”
Douglas established himself as co-captain Ben Carter’s partner in the second row after arriving from Biarritz in the summer of 2025, featuring in 19 of 25 matches.
Dragons have Seb Davies, Matthew Screech, Barny Langton-Cryer and Nick Thomas as other specialist options in the second row, while flankers Ryan Woodman and Shane Lewis-Hughes have previously covered lock.
Tiatia’s side travel to Treviso and then remain in Wales for the rest of a crucial first block of the season in their bid to build on an encouraging 2025-26.
Dragons have home derbies against Scarlets and Ospreys in the URC, a Challenge Cup opener against Perpignan, an away fixture against Ospreys at the revamped St Helen’s and then a Newport fixture versus Zebre.