The Real Madrid right-back sat out La Roja's 3-3 draw with Portugal in their opening World Cup match last Friday, as he was still struggling from a hamstring injury sustained against Liverpool three weeks ago.
"Dani is doing well," Hierro told reporters at his pre-match presser. "He has been training with the rest of the team for nearly one week so has recovered very well.
"He has been working with doctors, physios and the medical staff. He is available for tomorrow."
Carvajal was used 38 times for Madrid in all competitions during the 2017-18 campaign.