Puyol has endured an injury-plagued year so far, missing several games during his side's La Liga title triumph, as well as their run to a third European Cup final in six years.
Hernandez, on the other hand, has been one of the sensations of 2011, helping United clinch the Premier League title and reach their third Champions League final in just four years.
The Mexico striker, who moved to Old Trafford last summer, will be one of the few players unfamiliar to Puyol and his defensive cohorts ahead of the sides' fourth meeting in the last four seasons.
His movement would cause problems even to a fully-fit Puyol, never mind one with fitness concerns. But the Barça skipper said: "I feel great. The last game I played, I prepared for this and I'm ready and I can play. I'm fully fit.
"It is true that, because of my injury, I haven't been playing a lot over the last few months. When I played against [Real] Madrid in the semi-final, I hadn't played much either. I've trained even more now so I'm in a better position."
Puyol is looking forward to testing himself against the man they call 'Little Pea'. "He's an important player," he said. "He's always on the verge of being offside and he's also a scorer, so he's definitely a player to take seriously."
Coach Pep Guardiola added: "He's a huge surprise, he's amazing. He's amazing when arriving in the area. He has incredible movement without the ball. Manchester United has bought an enormous young player. I am convinced that he will be an important player for the next years at United."
If Barça play like they can, it will be difficult for Hernandez to see enough of the ball to be a threat. And the Spanish champions look in the mood to repeat their 2009 triumph over United, with Puyol keen to "have fun" at Wembley.
But his coach was not so sure, saying: "You have to compete well and you have to suffer a bit to win. We've been having fun but, from this point on, we have to give what we have to offer and not enjoy it."
Guardiola spent almost his entire playing career at Barça and was in the side that won the European Cup for the first time in 1992, at Wembley.
Responding to rumours his long association with the club could end after tomorrow's game, he said: "Today is not the day to talk about that. Leaving? We'll leave that for another day." Puyol added: "He's the best trainer in the world and this is his place. I hope he is here for many years."