Brown: Left low on Sunday
But he knows they have to put the shock defeat out of their system ahead of what could be a momentous Old Firm derby at Ibrox on Sunday.
Celtic can clinch the Scottish Premier League title with victory - provided Motherwell fail to beat Kilmarnock at Rugby Park on Saturday.
The earlier game will be a sombre occasion despite the fact Killie beat Celtic 1-0 on Sunday in the Scottish Communities League Cup final - news of midfielder Liam Kelly's father collapsing and dying in the Hampden stand overshadowed their triumph.
Brown told Celtic TV: "All the lads were gutted, especially when we heard the news about the kid's dad as well. It's such a shame.
"It's a sad occasion and we just wish his family and him all the best."
The Celtic players had Monday off but Brown admitted there was little prospect of relaxing following the cup loss.
"There's just so much going around in your mind - what I could have done, what I could have done better, what other players could have done and could other players have helped you out," the Scotland midfielder said.
"There are so many different situations going round in your head.
"It's hard to sleep after a game never mind a cup final. You just think about what you could have done and what you could have done to prevent the goal.
"It's a bad time now but when Sunday comes it's got to be out of our heads.
"It's a terrible defeat to take. It really hurt but we have got a league to win.
"We have a big game at Ibrox and it could possibly be the league winner."
Celtic will go into the match as favourites with Rangers suffering three defeats in four games since going into administration.
"It's just the situation Rangers are in now, but we know better than anyone going into a game as favourites doesn't mean you're going to win," Brown said. "That showed on Sunday.
"I know Rangers are struggling for players and have a few out but that doesn't mean the ones who play are going to give anything other than 100%.
"I think they will have a point to prove but it's us versus them and hopefully on the day we want it more."
