Messi was flattened by a physical challenge from Chris Smalling during United’s 1-0 defeat at Old Trafford in the first leg of the Champions League quarter final last week.
The incident left the Argentine ace with a bloodied nose and swollen face for the rest of the game.
Messi appeared to go into his shell afterwards and had little impact on the match, despite Barcelona winning to put themselves in the driving seat ahead of Tuesday night’s return leg in the Nou Camp.
Messi was rested for Barcelona’s weekend game with La Liga strugglers Huesca.
But Valverde insists Messi is fit again and raring to go, despite being left shocked by events at Old Trafford.
He said: “I don’t think he is worried about the same thing happening again.
“He is fine, he is perfectly fine after the blow he suffered. He was okay a couple of days after it.
“But he was a little bit stunned at the time, although he’s okay now for this game and ready to go.”
Valverde knows his side are in the driving seat and red hot favourites to book a place in the semi finals.
But he admits the one thing he fears most about United is their famous fighting spirit and he added:
“I don’t know what the team of United’s is going to do, but we do know that we have examples of what they have done in the Champions League away from home this season.
“Manchester United have a special thing. They won a European Cup in the last few minutes (1999) – so we have to keep that in mind.
“We know that our rival can go on the counter attack, so we cannot allow that. What I fear most is the spirit that they have.
“We respect them as a team for what they are and the history they have. You can feel their spirit on the pitch and we expect to see that here.”