"I was rubbish," he says in exaspaeration. The fact that the game was at Wembley, only weeks before the Champions League final was played at the ground, only exacerbated his annoyance with himself.
Mohsni played in central midfield for Southend United against Crewe Alexandria in the Johnstone's Paint Trophy final. He was brushed aside in the lead up to Crewe's second goal and missed a clear opportunity to pull a goal back, before being substituted in the 57th minute. Afterwards, the Southend manager Phil Brown remarked that he "will never know" how Mohsni missed the chance that fell his way.
"I didn't have any excuses," Mohsni said. "I didn't help the team at all. That was the most disappointed I have felt after a game. I would have been as much [use to the team] if I had been running around the outside [of the pitch]. On Monday after the final we watched a video back. It was 15 minutes long - and 14 minutes of me. It was a nightmare game. I was so happy to play at Wembley. My friend and my brother both came over, so the build-up was very exciting. But it wasn't a good game for me. I was just rubbish."
Moshni hopes to make amends, at least to his own sense of self-esteem, this season with Rangers. Reaching the Ramsdens Cup final is, in the grand scheme of the club's history, a minor event, but there is also an opportunity to progress to the latter stages of the Scottish Cup. Should Rangers prevail over Albion Rovers at Ibrox on Sunday, they will play the semi-final at their home ground, with Hampden being refurbished for the Commonwealth Games.
"I don't think we're favourites, we have other [top-flight] teams who are more favourites than us," Mohsni said. "But in a cup any team can beat any other team. Every player in our squad would like to face a Premierleague team to see what we can do against them. That's what we're looking for in the next draw if we get through this round on Sunday.
"We only need two more games to win the league. After that's over we can concentrate on two cups. It will keep us concentrated. We want to win the league unbeaten and every player in Scotland wants to win this cup. Lee McCulloch and the Scottish players here have emphasised how important this competition is.
"I can compare it to the French Cup, which is also very important to win. It would be great for the fans, the club and the staff - and for me, too. I would lose a couple of league games in exchange for winning the cup."