Man Utd: Keane slams ‘schoolboy’ Pogba
Pogba failed to provide the spark United needed as they crashed out of Europe's major club competition, losing 2-1 in the round of 16 at Old Trafford.
And former United captain Keane told ITV that manager Jose Mourinho faces a challenge to get the best from the club's record signing.
"He's not the only problem,'' he said. "But he is a big problem and if he can't get in the starting XI you're in trouble.
"He's come on and you expect good players to affect the game. He came on and did nothing. His reaction to the goal is like a schoolboy. He doesn't smell danger.
"The reason you're part of a team is that if one of your mates makes a mistake you cover for them, you make up for it.
"Nobody is helping each other. They are almost playing like individuals and not playing as a team."