Sakho made a deadline-day move to Anfield in search of regular first-team football, after consistently missing out to Brazilian duo Alex and Thiago Silva in central defence at PSG last season.
Alex believes that Sakho feared for his chances of playing for France in next summer's World Cup, while admitting that the centre-back is too talented a player to sit on PSG's bench.
He told ESPN: "He's a great player, he needs to play.
"It's a good choice for him because he has joined a great club. He wants to play the World Cup so he has to play.
"He's a player with talent and a future. It's a choice we understand."
The 23-year-old was left out of the Les Bleus squad for World Cup qualifiers last week, with Didier Deschamps citing a lack of match practice as the reason for his omission.
Sakho is in contention to make his Reds debut after a full week's training on Merseyside, with Brendan Rodgers yet to decide who will start when Liverpool travel to Swansea City on Monday night.