Sir Alex Ferguson has denied Javier Hernandez is suffering from a long-term brain condition after the Manchester United striker was hospitalised with concussion.
Hernandez was taken to hospital and kept in overnight after being struck on the head by a ball during a training session in New Jersey on Tuesday night.
The doctor at Hernandez's former club, Chivas Guadalajara of Mexico, claimed the forward has suffered from similar problems in the past and had received treatment for them.
However, United boss Ferguson said this was the first he'd heard of the possibility of a pre-existing condition, but said the 23-year-old would be given as much time as it takes for him to recover.
"I'm not aware of that," said the Scot, when it was suggested Hernandez had suffered from neurological problems in the past. "This is a straightforward concussion.
"He was hit on the top of the head with the ball in the early evening.
"When he was back at the hotel, taking his meal, he felt sick and he was sick. He had headaches, so we removed him to the hospital where he stayed in overnight.
"They did the MRI scans and that was all-clear. They released him yesterday and he travelled down [from New Jersey to Washington, DC] today.
"Concussion is something you don't want to happen but usually time heals that and we'll give Chicharito plenty of time.
"We won't be rushing him back. I'll only bring him back when the doctor tells me I can bring him back."
In reports from Mexico, Chivas' doctor Rafael Ortega said Hernandez had fallen victim to acute migraines.
"I remember in his time as a youth player, he suffered from acute migraines," said Ortega.
"Originally it manifested itself as a headache, but afterwards the symptoms disappeared.
"We had some studies done on him but that was six years ago and he has done well since.
"I don't know if there is a connection between the two situations. I'm not up to date with the current situation, we would have to speak to a neurologist.
"I don't know if this can affect him in the future. I'm sure United will send him to a specialist and the situation will be resolved."
Hernandez, who scored 20 goals in his debut season last term, was taken ill at the team hotel and was rushed to hospital after he began vomiting.
After spending a night under medical supervision, and a series of tests, Hernandez was allowed back to the team hotel.
He missed United's 4-0 win over an MLS All-Stars team on Wednesday and did not fly with the squad to Washington DC yesterday, instead being driven the 250 miles to the final destination of the tour.
United take on Barcelona tomorrow in a re-run of last season's Champions League final, which Pep Guardiola's Spanish side won 3-1.
"Barcelona's performances and feats over the last two or three years have elevated them in everyone's mind. They're the best team currently in the world," said Fergie.
"I'm quite happy to be in second place at this moment in time, because it means we are the nearest challengers to them.
"Our challenge is to get to that level. It's not just about the football team - it's the philosophy, what they believe in, how they coach, how they produce young players.
"We have the same drive ourselves to produce young players. If I thought they'd play all their young players on Saturday then I'd play all mine and it would be a fascinating game."