Brown is struggling with a hip injury while Forrest has a tight groin and both will be assessed on Saturday morning.
Striker Mo Bangura is out with a thigh injury.
Neil Lennon has warned the rest of the SPL that his strongly-fancied Celtic side will not be victims of complacency this season.
The Bhoys are overwhelming favourites to retain their SPL title now that Old Firm rivals Rangers have been re-launched in the Third Division. Hearts boss John McGlynn claimed that the only way Celtic could be threatened would be if the champions took it too easy.
Lennon, speaking at the club's Lennoxtown training complex ahead of tomorrow's SPL curtain raiser against Aberdeen at Parkhead, said: "It might be a fair comment but it is not going to happen. We pride ourselves on our professionalism and our standards that we have set over the last couple of years and we want to maintain that."
He added: "Allied to that, we want to get through the next round in Europe and have a go at European football on top of the domestic league but there will be no complacency, that's for sure.
"We go into the season as favourites which is something that we are used to now.
"We are probably heavier favourites than we have been for a while but we will just concentrate on retaining the title, that is the priority.
"We had a great campaign last year, we are looking forward to tomorrow and the symbolic gesture of having the flag unfurled at the stadium which is always a nice occasion for everyone involved and then we get cracking."