The Arsenal defender has been criticised following the north London side's 3-2 defeat to Olympiakos.
Indeed, Nicholas criticised several figures after the north London club's embarrassing defeat - with their manager chief among the culprits.
But two in particular the Sky Sports pundit and ex-Arsenal forward singled out were Per Mertesacker and Gabriel.
Nicholas told Sky Sports after the game: "The first goal is a deflection but the second one is a basic corner. He's not under any pressure and all he's got to do is catch and hold it.
"Even though Sanchez gets them back into it, the third goal is shambolic. Gabriel is slack and slow and Mertesacker is not quick enough to cover."
What has Gabriel brought?
Since coming to Arsenal in January, Gabriel has ultimately underwhelmed. The 24-year-old was supposed to give boss Arsene Wenger another option and solid back-up at centre-back. He was also supposed to get the most out of Mertesacker through providing increased competition.
Right now, though, both Gabriel and Mertesacker are underperforming and, even when the Gunners are beating sides by scoring five goals, their defence is all over the place.
It's the same old from Arsenal, which means Wenger will probably somehow guide his team out of the Champions League group stages - just so that he can ensure he stays as long as possible, continuing to disappoint time after time.