Naismith admits the whole team were gutted to lose the goal which leaves the Scottish champions rooted to the bottom of Group G and facing a massive battle to book their place in the knockout stages.
He revealed how Novo, in particular, was devastated by the role he had to play in second-placed Unirea claiming a share of the points.
But he insists Rangers must now look ahead to their remaining two games against Stuttgart and Sevilla.
"Nacho is obviously disappointed with himself and he was pretty down in the changing room," Naismith told the club's official website.
"But everybody here is just gutted at the result to say the least. We played really well throughout the game. To lose the goal as late as we did was hard to take.
"We knew we could get a result here and I think we showed with our performance that we deserved a win.
"Things went perfectly for so long and it's just one late, late mistake which has cost us in the end but we have to move on now."
Rangers move on to Scottish Premier League action against an improving St Mirren side.
Saints suffered a setback when they lost 2-0 to Hamilton last weekend but they had netted 11 goals in their previous four games.
And in-form midfielder Andy Dorman is relishing the trip to Govan.
"It's a game we definitely look forward to," Dorman said. "It's a great stadium to play in and obviously a good team to play against.
"We have to go out and be positive and stamp our style of play on the game.
"We feel like we can score goals no matter who we play against."
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