The Blues forward, who made such an early impression with the club, picked up the injury during training and now faces a spell on the sidelines.
Speaking to the Southend Evening Echo Blues boss Steve Tilson said: "It's very disappointing for both Francis and ourselves. He just went over on it during training and you just can't believe it's happened. It's too early to say exactly how long he's going to be out but you're looking at anything from two to six weeks."
The injury means Laurent will miss the weekend clash with Crewe as well as next Wednesday's FA Cup replay with Chelsea.
It's a blow to Tilly as offers something different from the other strikers, especially when coming on as a sub late on.
Meanwhile, Damian Scannell is back at Southend United after a disappointing loan spell at Brentford. The winger made only two appearances while with the Bees.
Tilly continued: "Damian didn't get as many games at Brentford as him and ourselves both wanted. They had a player who they thought was going to be out injured for a little while but came back quicker than they thought. That meant Damian only started one game for them and he's back with us."
Scannell, who started the season in the starting line-up for the Blues before falling out of favour, has now resumed training with the team. Might replace Laurent on the bench against Chelsea.
The Invisible Man Richie Foran, well at Roots Hall anyway, is also back with Southend after two months on loan at Darlington where he scored three goals in 13 games.
There's no quote from Tilly here, expect him out again as quickly as he came back. Will not replace Laurent on the bench against Chelsea.