Gordon Strachan admitted that Celtic have left themselves with “a mountain to climb” if they are to have any chance of reaching the Champions League’s last 16 for a third successive season following the 1-0 defeat by Villarreal in Spain last night.

Strachan found himself having to explain away yet another loss away from home in the competition, which leaves Celtic with one point from two games and mired in trouble behind Manchester United and Villarreal in group E.

Last night’s defeat, following Marcos Senna’s vicious second-half free kick which gave Artur Boruc no chance, leaves the stain of Celtic’s away record in Europe intact. In 16 attempts now in the group stage of the tournament the club have failed to record a win, and that run stretches to 18 games if you count two away legs in the last 16. It is a curse Celtic cannot shake off.

“It is going to be right hard work now — we have a mountain to climb,” Strachan said of Celtic’s chances in the group. “We’ll just let things pan out and see what happens but it is going to be very hard.

“But what I’ve said to people is that at least we showed tonight that we can play at this level. We did all right in parts of the game and we worried Villarreal when we had the ball. But it’s just unfortunate that we faced one of the best teams in Europe right now.

“Tonight was still the most comfortable we’ve been away from home [in Europe] in my time here. I thought we were able to create things.”

The Celtic manager appeared to dispute the free kick, given away by Paul Hartley on Joseba Llorente, which led to Villarreal’s winning goal after 66 minutes. The television replays were not conclusive about Hartley’s tackle, though many thought that the referee, Viktor Kassai of Hungary, called the decision correctly. Senna duly stepped up and swerved the free kick past Boruc.

“The players are not convinced it was a free kick,” Strachan said. “But only the player who was involved in it [Llorente] will know if he dived. I can’t point the finger at anyone, that wouldn’t be right. But the pictures themselves tell you.

“I asked the players to perform tonight — I wanted a performance and I feel that I got it. I don’t think that anyone would disagree that our first-half performance was excellent. We were reasonably comfortable, but then after about 55 minutes Villarreal started working in areas of the park which caused us problems. Because of that, we couldn’t keep the ball, and once they went 1-0 up they showed what a good team they are. And in Senna they have a world-class player. That was obvious tonight.”

Manuel Pellegrini, the Villarreal coach, unsurprisingly thought that the Senna free kick was correctly given. “I thought it looked like a foul,” he said.

Celtic now face Manchester United at Old Trafford in three weeks’ time on a make-or-break night in the group. It could be that a consolation Uefa Cup place looms.

“I still think the players can be pleased with their efforts,” Strachan said. “We were rarely in real pressure situations, though the result is obviously disappointing.”