The revelation comes after six men in the UK were arrested on Wednesday on suspicion of match-fixing, with the Conference Premier club's boss stating he felt something was "not right" about the match in question.
Simpson, who confirmed the game was not during his tenure at Lincoln, added that it was a "worry" for football in the UK and said he did not know how authorities would tackle the issue.
"I must admit I have been involved in games where you think something is not right and I certainly flagged one of them up," he told The Lincolnshire Echo.
"I don't know how they are going to get around it or how they are going to stop it. You seem to be able to bet on anything these days. It is certainly a worry for football and for the game in this country.
"I was involved in a game, I don't want to say where it was, but there were two penalties given against us. I was told there had been an irregular betting pattern on it during the game and before the game.
"I flagged that up. We heard from the authorities that it was correct and there had been an irregular betting pattern in the game.
"We lost the game and we ended up having a player sent off. To this day it's the only game I have been involved in where I have thought there was something wrong. This was not while I was at Lincoln City."
Clubs in the Conference South, a division below Lincoln's league, were asked to remind players and officials of their responsibilities earlier this year after what the FA described as "suspicious betting activity" involving a number of matches in the league.
In a statement on their website, the Football Conference said on Thursday it had "become aware of a story published today concerning arrests being made over alleged match-fixing".
"The Football Conference takes all matters relating to the integrity of the game very seriously but it cannot make any comment on today's story as it would be inappropriate to do so," they added.
