Manchester United and Liverpool have issued a joint statement condemning an attack on the ambulance that transported Alan Smith to hospital.
The England international suffered a badly broken leg and dislocated ankle during United's weekend FA Cup defeat to Liverpool at Anfield.
He was immediately rushed to hospital, but some Liverpool fans attacked the ambulance during its journey away from the ground.
"These people aren't real fans of football," United and Liverpool said in the statement.
"Both clubs feel the mindless actions of a few idiots should not overshadow the efforts of all involved to make sure Alan received the best possible treatment as soon as possible.
"Manchester United would also like to point out they are very grateful for the speedy and efficient help of all Liverpool staff."
A spokesman for the Merseyside ambulance trust confirmed the attack, saying: "It did not result in any delay in transferring the player to hospital but the trust cannot condone this type of behaviour while administering emergency treatment."