The Daily Star says Grant blew his top in an amazing 20-minute training ground rant ahead of the contest against Arsenal which left most of the club's big names stunned.
"He's adopted a pretty much softly softly approach since taking over and maybe a few of the players had started to become a bit complacent.
"But he was clearly fed up with things and said he could baby-sit the players no more and that it was time they started taking responsibility for things themselves.
"There may have been some in the squad who doubted whether he had the bottle or the backbone for the job but after that blast they are in no doubts he means business now."
The source added: "He said he felt there were some who were happy to hide behind others or excuses when things went wrong, but everyone should be in it together in good times and the bad."