The former Manchester City manager is impressed by the attitude of the Celtic players.
They have three away goals to their name for the second leg at the San Siro, however, Celtic's incredible fightback last week leaves Inter boss Roberto Mancini in no doubt that they are in for another battle this evening.
"It's not going to be a simple task.
"We need to have total concentration and not give anything away. Celtic are a team that never give an inch."
The former Manchester City boss would have known about Celtic's legendary grit and determination in European competition already from his time in England - but he saw it first hand last week.
After going 2-0 down The Bhoys stood up. A goal from new signing Stuart Armstrong put them back in the game and then an own goal from Hugo Campagnaro saw them level one minute later.
Rodrigo Palacio looked to have won it for the Italian giants. However John Guidetti smashed hom a 90th minute equaliser to claim an epic draw against Inter.
Celtic know that for them to qualify they need to win in Italy, or draw an unlikely result 4-4 - so the odds are stacked against them.
But Mancini knows, as well as everyone knows, that is when Celtic are at their best.