The Spanish winger came on as a second-half substitute in the Swans' goalless draw with Sam Allardyce's men after recovering from a two-month lay-off with a thigh injury.
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"I feel okay," he told the South Wales Evening Post. "I could have played for the last few weeks. This injury should have only lasted two or three weeks but when I started training I felt a problem in the same leg.
"I had to restart the treatment so it ended up being a long time.
"It's fortunate for me that on Sunday I could play 30 or 35 minutes.
"I felt good on the pitch and I will train hard this week ready for the next game. Now I need more minutes to rebuild the confidence.
"I think I should be able to train normally all week with the team and hopefully I'll be ready to start, but it's not my decision."
Hernandez, who has not started a Premier League match since a goalscoring performance in Swansea's 2-0 victory at West Brom, is well aware of what the derby fixture means to fans of both clubs.
"It's a difficult game," he added. "Both teams want to win the match, Cardiff are at home but we want to win this for the fans. The occasion should be unbelievable."