The Scottish champions host Spartak Moscow in their final Group G game needing to pick up maximum points at Parkhead to stand a strong chance of progressing to the last 16.
The Hoops were held to a 1-1 draw by second division side Arbroath in the Scottish Cup on Saturday, and Forrest says that there is no time to dwell on that result.
"It's good if you've got two games per week," he said. "If you get a bad result it means you can rectify it two or three days later by getting a good result in another game.
"The boys are over the weekend game now and hopefully we can take care of Arbroath when the replay comes around next week.
"The boys are full of confidence for Wednesday night and that's the main thing.
"We've got the squad to play in all the competitions and we know we can cope in them all.
"All the boys have got faith that they can get through to the last 16 and get a good result on Wednesday.
"We've not been in the Champions League for the last few years so it would be a massive achievement."