The Inter Milan boss's comments follow a poor 2015 so far...
Speaking after a late 1-0 defeat at Napoli, Mancini was left livid by his side's defending. And the Italian is irked by how exposed the Serie A outfit are defensively when going forward.
"You just can't concede a goal like that," Mancini said. "I'm shocked.
"The goal we let in was absurd. We shouldn't have lost this game. We played really well throughout the game but, every time we go and hand the opposition a free goal. We were far too lax."
Doesn't that sound intriguing for Celtic...
Ronny Deila's side face Inter in the Europa League later this month and, considering the Italian side's recent form, the Bhoys appear to have every chance in the world of pulling off a dream European victory.
Inter have lost their last three on the bounce, being outdone by Napoli, Sassuolo and Torino, and have suffered a mediocre 2015 to date - picking up just two wins in seven (they were unbeaten in four but these last three losses have done the damage).
And Mancini's public criticism of his side leaves the door open for Celtic to counterattack their way towards inflicting even more hurt on the struggling Italians.
Will Deila, though, heed the calls - or will Celtic go all out attack and play the way the manager has emphasised throughout the campaign?