Fellaini clashed with Can in the closing minutes of the game but the incident was missed by all six match officials.
“If the referees had seen that, it would have been a red card for sure,” former Premier League referee Howard Webb told BT Sport.
“Uefa might want to look at that as well, it was clearly an act of violent conduct, none of the six officials saw it on the day.”
Liverpool would have scored again were it not for the heroics of United keeper De Gea who faced eight shots on target and made a string of remarkable saves.
United are now without a win in their last six knockout games in all competitions but will have the chance to redeem themselves in the second-leg at Old Trafford next week.