The Scottish champions suffered a second successive loss in the competition as Martin O’Neill’s side were beaten 4-1 in Lisbon, leaving them without a point from their opening two league-phase fixtures.

But Nygren remains adamant Celtic can turn their European campaign around with six games still to play. He said: "Yes, that's what you always have to believe.

"It's still six games to go so it's in our own hands."

Celtic found themselves 3-0 down at half-time against Benfica before showing greater attacking threat following the restart.

Nygren was introduced in the 57th minute, shortly before Camilo Duran pulled one back, and the midfielder admitted he briefly believed a comeback could be possible.

"You always have to believe," Nygren continued. "In the second half when I was on the pitch and we scored, I thought we could come back into the game.

"I thought we had momentum. I thought we played better than the opposition at that time so I always believed.

"We got a goal and played a bit better but the first half was a bit difficult to watch because we were down 3-0."

Celtic now have to quickly turn their attention back to domestic matters, with Hearts visiting Parkhead on Sunday amid a demanding run of fixtures.

Nygren, though, insists playing regularly in major competitions is exactly what Celtic players want. "It's difficult to say," he said when asked about the impact of the schedule.

"When you're a Celtic player you want to play in the biggest competitions in European football, so you want to play those games. But like you say, it's a lot of games, that's how it is. We're pretty used to playing every three or four days.

"Unfortunately we didn't win tonight, but we played a good side, so we just have to focus on the next game and to win that game."

That next challenge carries extra significance, with Hearts returning to Celtic Park for the first time since last season’s dramatic title decider.

Nygren remembers that occasion fondly and expects Hearts to arrive with no shortage of motivation. "Of course, I think they do every time," he said.

"I think all teams do when they come to Celtic Park and play us. Last time we played was a very special game, a game I will never forget. It was a great day and a great ending.

"It's a big game, a very important game, so I'm looking forward to it."