Defender Pogba, a Guinea global, joins the club from Turkish side Genclerbirligi.
"He was huge in the first games played with the new coach - in the physical dimension, in his ability to break lines, to carry the ball forward, to weigh into the penalty area, to score".
"We're pleased to officially welcome Florentin to our club", Atlanta United VP and technical director Carlos Bocanegra said in a statement.
Florentin, born in the Guinean capital Conakry prior to his parents' move to France, started his career with French side Sedan before switching to St Etienne in 2012.
Pogba has earned 21 caps for Guinea and spent almost a decade in Ligue 1, mainly with AS Saint-Étienne.
The Norwegian's arrival has brought a renewed positivity to the club, but midfielder Herrera, 29, has warned his team-mates they can not afford to get carried away ahead of the first leg of their last-16 Champions League tie against Paris Saint-Germain next Tuesday and should forget about records.
Internationally, Pogba represents Guinea and made his debut as a 19-year-old against Mali on August 11, 2010.
Paul has become an worldwide superstar following a then world-record £89million transfer back to Old Trafford from Juventus and World Cup success with France, but Florentin has taken a more sedate route around the football circuit.
Ole Gunnar Solskjaer will have a big say in Manchester United's plans for the summer transfer window even if he leaves Old Trafford, according to reports in the British media. Benitez, who recently debuted for the Canaleros against the US, signed with ATL UTD 2, Atlanta United's second team, from Plaza Amador.
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