Now he has urged his team-mates to pick themselves up for their remaining three Champions League qualifying matches as he believes the Parkhead club have shown they are serious contenders to reach the knockout stage of the competition.
Hot on the heels of his eventual inclusion in Roy Hodgson's England squad, the Hoops shotstopper was in magnificent form as he pulled off a terrific double-save from Lionel Messi as well as other top-drawer stops to keep the Barcelona hitmen at bay.
In the end, it wasn't quite enough as the Spanish giants netted a 94th-minute winner to secure the three points, but Forster says his team-mates have every right to be proud of their efforts and reckons they have to approach the second half of the group with optimism.
Next up for Neil Lennon's side is the visit of the Spanish league leaders to Parkhead a fortnight tonight, and the keeper said: "I think we have shown we are capable of taking points off the other teams if we play well enough on the night.
"Certainly, if we play as well as we managed against Barcelona last night at the Nou Camp then we'll have a good chance as we gave it everything we had and were really unlucky not to have earned a draw from the game.
"We'll now look forward to playing them at Celtic Park although we know it will be another huge test as they are possibly the best team in the world and we also face a tough game away to Benfica before playing Spartak Moscow at home. But we'll definitely be giving it our best shot."
Forster says he knew Celtic were on the verge of pulling off a major shock and was left cursing his luck as Jordi Alba drifted in at the back post to poke home the winning goal.
He added: "We just had to defend one more cross. Unfortunately, we weren't able to do that and they scored. The feeling inside the dressing room immediately after the game was one of devastation as we were so close to getting a fantastic result. I don't know exactly how long there was remaining, but you are talking seconds. That's how close we were.
"I think we deserved a point out of the game for the way we performed. When you play against Barcelona there is going to be a lot of defending, which there was, but we did that so well and everyone worked so hard and put so much into the game. It's nice to make saves, but they didn't count for anything because we lost the game."