Hearts arrived at Celtic Park with the recent 7-0 hammering from the Hoops in the Scottish Cup still fresh in the memory.
And the visitors provided stubborn resistance on this occasion as they defended in depth before Kris Commons struck on 63 minutes, and Hearts were still in the match until James Forrest scored in stoppage time.
Mjallby believes the Celtic players and management need fresh focus after being knocked out of the Champions League - the first of which is to go another four league games unbeaten in the league.
He said: "Obviously there is not going to be any more European football this season, so we have to set new targets and incentives for the players.
"Being unbeaten is going to be very important for us and obviously right now, the target is to go 20 games unbeaten and then we take it from there.
"You always look for progress and to do better. Being knocked out of Europe was disappointing but the first target was to get there and hopefully get the same run as last year (last-16 appearance) - but it is quite hard because you are fighting against teams who have bigger financial muscle."