Shakespeare watched City draw their fourth straight home game 1-1 against the Hatters on Tuesday.
They are still 12 points clear at the top of the table, but third-placed MK Dons can narrow the gap to four points if they win their three games in hand.
"Are we worried? No. Concerned or frustrated? Yes. But we have great faith in these players," said Shakespeare.
"It is a bit frustrating, we would have liked to have won but it is another point towards the tally which will get us promotion. We would have liked to have turned some of those draws into wins, but we have still got 11 games left to do that.
"We are getting to the business end of the season now with most teams you play fighting for points, whether it be for a play-off place or fighting relegation."