Police are investigating death threats made to the Reading players involved in incidents in which Chelsea keepers Petr Cech and Carlo Cudicini were injured.
Ibrahima Sonko and Stephen Hunt have received a series of letters at the club's Arborfield training ground.
Thames Valley Police told BBC Sport: "The club is helping us with inquiries and the matter is being investigated."
A Chelsea spokesman added: "There is nothing to suggest these threats came from genuine Chelsea fans."
"The club is dealing with all my letters and I don't want to say any more"
According to the Reading Chronicle newspaper, one letter said: "We are going to kill you for what you did to our players."
Reading players treated the first letter as a joke and pinned it up on the door of the training ground dressing-room.
But when subsequent letters arrived, players were told to treat the threats seriously and the club called in the police to investigate.
Cech is not expected to play again this season after sustaining a fractured skull in a first-minute collision with Hunt in the game at the Madejski stadium on 14 October.
Cudicini needed oxygen after being stretchered off in a last-minute collision with Sonko, and only recently returned to action.
Chelsea boss Jose Mourinho hit out at Hunt's challenge, but neither Hunt nor Sonko faced any sanction from the Football Association.
Winger Hunt, on international duty with the Republic of Ireland, said: "The club is dealing with all my letters and I don't want to say any more."
Sonko confirmed he had received a letter but made no further comment.
Chelsea's spokesman said the club had not been contacted by the police regarding the matter and added: "Naturally, we condemn any threats of this nature and we will assist the police fully if - and we stress if - there is any evidence linking these threats to any of our supporters.
Reading boss Steve Coppell played down the death threats.
"We wanted to keep it quiet, and didn't make an issue of it. We went through the proper channels and hoped it would die a death. To regurgitate it now is of no benefit to anybody.
"I don't think it's for public consumption. It's something different for the media to report but it serves no purpose to anybody else."