Mohsni could make his United debut when Dunfermline visit Tannadice on Saturday after signing until the end of the season.
The Tunisia international served a seven-match ban in France after punching and kicking Lee Erwin and struggling with several other Motherwell players following his final game for Rangers in May 2015.
But Laszlo moved for the centre-back on the advice of new assistant Paul Sturrock as he looks to turn around form which has seen United win two out of nine Ladbrokes Championship games, conceding 18 goals in the process.
“He has a bad boy reputation and he can stay a bad boy for me,” Laszlo said. “The most important thing is he plays good football, shows aggression and can help the team.
“I don’t want to change Bilel’s character, I just want to use his ability for the team and be a mature, experienced leader.
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“If you look at the table, the numbers don’t lie. We are conceding too many goals so we need to stabilise the defence, so he is here for this reason.”
United will have Emil Lyng back from injury but Jordie Briels remains on the sidelines along with long-term absentees Scott Fraser, Fraser Fyvie, James Keatings and Lewis Toshney.
Right-back Anthony Ralston made his debut on Tuesday after joining on loan from Celtic but failed to prevent United falling to a 3-2 home defeat by Queen of the South and Dunfermline boss Allan Johnston is aiming to take advantage of an unsettled United side.
Johnston, who is likely to be without Joe Cardle (ankle), said on his club’s official website: “They’ve changed their team about a fair bit as well. There’s been a lot of changes, a couple of changes every week. I see they’ve signed Mohsni as well, Ralston played in the last game.
“There have been a lot of boys coming in, new players and maybe boys who haven’t been playing every week. That is difficult sometimes and we’ve got to try to take advantage of that.
“I’m sure after the result this week they’ll be looking to make changes again, so hopefully we can be on the front foot and get the three points we all need.”
With St Mirren not playing because of the Irn-Bru Cup final between Dumbarton and Inverness, Livingston can close the gap on the leaders to nine points if they win away at Queens, who hope to have Stephen Dobbie back in their squad but will be without the suspended Darren Brownlie.
Morton will be without the suspended Gary Harkins as they host bottom club Brechin while manager Jim Duffy is considering sending club captain Lee Kilday out on loan after the defender played his first 90 minutes in 10 months in an under-20s match as he continues his comeback from ankle surgery.
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