Mohsni was a shock inclusion in United's side for Saturday's 2-1 home defeat to Northampton as he made his first appearance for the club this season, although he was back to his mercurial best, showing glimpses of quality before seeing red for a high challenge in the 27th minute.
The Frenchman, 25, has been at the centre of several disciplinary issues during his two years at Roots Hall and refused to return to the npower League Two outfit last summer, despite being under contract until the end of this season.
Several trials at a handful of other clubs followed before in October he agreed a three-month loan deal with Ipswich, who opted not to extend his stay in January, leaving the player in limbo.
But Shrimpers boss Paul Sturrock, speaking ahead of Wednesday's Johnstone's Paint Trophy area final second leg against rivals Leyton Orient, has handed Mohsni a lifeline and said he will stay until the summer.
"Bilel has come back to the club and he will remain with us for the rest of the season," Sturrock told Southend's official website.
"He looked very good on Saturday up until he got the red card which he was a bit unfortunate with. Both he and their lad went in high, but Bilel was just a bit late. We won't be appealing the card because I've looked at it from four or five angles and it's hard to argue with it.
"But he's in with us and is training and will remain with us. Once he has served his suspension he will be available for selection again."
Mohsni said: "I want to help Southend get promotion and hopefully a win at Wembley and really show fans what I can do.
"I know some fans are upset with what has happened and getting this red card hasn't helped. But hopefully I can do well in the games when I come back and help the team get some good results to help everyone like me again."
- Sports & Recreation