The charge threatens to earn the Danish keeper a suspension during the closing weeks of the League One season, but Ken Bates offered his support to Ankergren by claiming he "had to withstand a barrage of abuse all afternoon".
Bates urged the FA to follow up Ankergren's charge by reviewing the conduct of Swindon's fans and the governing body today confirmed that they are preparing to look into the behaviour of the crowd at the County Ground.
An FA spokesman says in the YEP: "We are investigating the conduct of the Swindon supporters. We have been awaiting the conclusion of police inquiries before pursuing this."
Ankergren is alleged to have thrown the object into the stand behind his goal moments after referee Chris Foy blew the final whistle at the County Ground.