The experienced 32-year-old collected the 12th ATP singles title of his career when he defeated Fabio Fognini 6-0 6-3 in the final of the ATP 250 clay-court event 12 months ago.
Robredo returns to Croatia for the 25th instalment of the tournament as part of a strong field and he does so having hit a recent blip.
There was no sign of his recent trouble when Robredo reached the fourth round of Wimbledon for the first time in his career before eventually being defeated by eventual finalist Roger Federer.
However, since then Robredo has exited his subsequent two tournaments prematurely, losing in the second round of the Swedish Open to Renzo Olivo before suffering a third-round setback to Lukas Rosol at the Hamburg Open last week.
Despite the defeats, Robredo is a fierce competitor on Tour and, with 11 of his career singles titles coming on the red surface, he is sure to be considered among the contenders.
Home favourite Marin Cilic lost the 2011 final to Alexandr Dolgopolov before triumphing himself 12 months later to become the first Croatian to win the event.
Both men are once more among the field and gunning for a second success, while Fognini returns in an attempt to go one better than last year.
And tournament director Vanja Bozickovic welcomed the strong line-up.
"For many players on the ATP World Tour the Umag-based tournament is one of their favourites," he told the tournament's official website.
"Alongside [past] Umag winners and finalists the tournament will welcome Italian Andreas Seppi, Austrian Jurgen Melzer, Argentinian Carlos Berlocq and Colombian Santiago Giraldo, among others."
Borna Coric, Mate Delic and Ante Pavic have all been handed wildcards for the tournament and will look to produce a shock at their home tournament.