Milan: Former Manchester City manager Roberto Mancini believes AS Roma can pull off a Champions League shock today, if they play to their full potential against the English champions.

Roberto Mancini
Roberto Mancini 

Roma's 5-1 rout of CSKA Moscow in their Group 'E' opener, coupled with City's defeat to Bayern Munich, has left Manuel Pellegrini's side desperately needing three points.

Mancini is currently without a club having departed Galatasaray at the end of last season — and that has given the former City boss time to keep a close eye on football in England and Italy.

"The key (for Roma) is to counter quickly and seize any chances City might offer. Roma need to be vigilant in defence, keep focus for the full 90 minutes and be clinical in attack," Mancini told sports daily Gazzetta dello Sport.

"A full-strength Roma can beat City, but the absences of (Daniele) De Rossi, (Leandro) Castan and (Davide) Astori could make them more vulnerable." Roma will likely be without Italy midfielder De Rossi due to a torn calf muscle, while Astori and Castan are still recovering from injury.

PSG without Zlatan
Meanwhile, Paris Saint-Germain star Zlatan Ibrahimovic will miss today's clash with Barcelona at the Parc des Princes due to a nagging heel problem, the French club have confirmed.