Imps boss Steve Tilson told BBC Lincolnshire: "Mustapha is a decent player and he would have done well for us in the Conference.
"You have got to have players that want to play for the football club but he wants to play at the highest level."
The Imps boss also confirmed that he is still in talks with defender Dany Hone's agent.
The 21-year-old, who is out of contract, was offered a new one-year deal at the end of last season.
"He is after a bit more money. I am keen to keep Dany but I have a budget that I have to work to," said Tilson.
Source: BBC Sport
Source: BBC Sport