McCoist had hoped to strengthen his Gers squad further by signing centre- backs Boris Pandza and Marius Zaliukas this week.
Bosnian internationalist Pandza had been highly recommended by former Light Blues left-back Sasa Papac.
Ex-Hearts stopper Zaliukas, meanwhile, had impressed during a succesful trial at Murray Park earlier this month. But both players opted not to sign for the SPFL League One leaders.
Pandza has joined Polish club Gornik Zabrze while Zaliukas has gone on trial at Sky Bet Championship club Queens Park Rangers.
Mohsni, though, is confident Rangers have enough strength in depth at the back to cope with the challenges that lie ahead this season.
And he has assured his gaffer his focus is firmly on defending even though he is always keen to charge upfield and attack.
The French-Tunisian has scored two goals - against Arbroath in the league and Queen of the South in the Ramsdens Cup - in his three appearances so far.
He said: "Yes, I like to get the ball at my feet and go forward whenever there is the opportunity for me to do that.
"I used to play in midfield when I was younger - before I grew to the size I am now and moved back to defence - so it is natural for me to do that. But I only do so when one of my team-mates is able to drop back into defence and cover for me so that the team is not left exposed in my absence. And I always try to do something useful with the ball.
"Nobody, the manager or my team-mates, has told me not to do so. I think they are keen to encourage me to play my game.
"It has been good to do that and also to score some goals for the team.
"I didn't really score goals at the clubs I was at before. But I think that was because I wasn't as settled at those clubs as I am at the club now. I am very happy here."
Mohsni added: "But I know I am a defender and my job here is to defend. It is nice to score goals and help the team out that way but I get a lot of satisfaction from keeping clean sheets.
"We have managed to do that as a team in two of the games that I have played in. The only goal we have let in - against Arbroath - was an amazing goal as well.
"But we take great pride in how we defend. I know that at this club we have to win every game that we play in whether it is in the league or in the Ramsdens Cup and that means defending as well as we can and keeping clean sheets in every match.
"I know that the manager has tried to bring in more players at centre-back. But that is good for the club. The more quality players the club can have then the better it is for us.
"It helps to create competition for places. But there are a lot of very good players here already."
Mohsni has formed a strong partnership at the back with Rangers captain Lee McCulloch in the first-team games he has been involved in so far in the 2013/14 campaign.
The 26-year-old has enjoyed playing alongside the versatile veteran and believes he can improve greatly as a player from working with him.
"He is a clever footballer," he agreed. "He can play at the back, in midfield or up front.
"That says a lot about what an intelligent player he is that he can do that. He has scored a lot of goals for us this season.
"There is a very strong squad here at the club with a lot of good players.
"There is a good atmosphere in the dressing room as well and Lee is a big part of that success.
"Hopefully we can continue to work well together and keep clean sheets and help the club to win games. I am enjoying playing with him."
McCulloch has scored the majority of his goals this season with his head - including a hat-trick in the 5-1 win over East Fife at the end of last month.
Mohsni, who is hoping to line up against Stenhousemuir in the League One game this afternoon, also prides himself on his ability in the air in both attack and defence.
And he is looking to punish opposition teams at set-pieces more and give the Light Blues supporters who are packing out Ibrox despite their team being in the third tier something to shout about.
He said: "I am tall so I am expected to win balls in the air. I will try to help the team out whenever we are in a position to score.
"It's always good to give fans something to shout about. I enjoy playing in front of such big crowds.
"I played at Wembley last season with Southend and there were over 40,000 fans there.
"But Rangers get those crowds at every home game. It is great to be a part of that."