On Saturday Palace chairman Steve Parish described Roberts’ challenge as «the most reckless I’ve ever seen» and that he «endangered a fellow professional and maybe his life».
On Monday Millwall said reporting of the incident «contributed to an unwarranted character assassination» of Roberts.
Millwall said he contacted Mateta after the match «with an apology which was accepted immediately».
Roberts served the first game of his ban as Millwall lost 2-0 to Bristol City in the Championship on Tuesday.
Millwall supporters showed their support by holding a minute’s applause after eight minutes and singing «there’s only one Liam Roberts». There were also some boos.
Michael Oliver, who refereed the game, will not be involved in a Premier League match this weekend.
He sent Roberts off after intervention from the video assistant referee (VAR).
