PAUL LE GUEN, the former Rangers manager, has insisted Celtic have no chance of European success and even risk losing the league title next season if they do not properly strengthen in the summer.

The Frenchman was working for television at Hampden on Sunday, his first time back in Glasgow since his ill-fated stay at Ibrox, and was surprised by how the Premiership champions-elect performed in their Scottish Cup semi-final defeat.

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Le Guen is aware of what has been going on over the last four years or so but it was the future he wanted to focus on and warned that unless the Celtic board realise money has to be spent in the next transfer window, they would be asking for trouble.

"This was the first time I’ve watched Rangers or Celtic this season – but it’s obvious that Celtic will need to improve," said Le Guen. "Without getting in a few new players, Celtic will not be able to compete in Europe and they might not even win the league. That’s obvious.

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"I think it’s logical to say that Celtic have dropped their standard. That is normal, that they would not spend so much money without Rangers there to push them.

"But when they meet together, they still produce suspense. I enjoyed it. I hope that people back in France enjoyed watching it, too.

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"I am sure that, with the comeback of Rangers, Celtic will have to compete with that. They have to respond. Maybe if Rangers also qualify for Europe by winning the Scottish Cup, they will get a real lift."

Le Guen has never had a bad word to say about his short time at Rangers which ended halfway through the 2006/07 season following a breakdown in his relationship with senior players, most notably Barry Ferguson who he sacked as captain.

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And while he was full of praise for the way his one-time club played in their victory via a penalty shoot-out, he urged the board at Ibrox and they too must spend.

"To be honest, Rangers will have to add some new players also," he said. "Kenny Miller is still a great player but he isn’t getting much younger. They need something to boost the team, some good signings. I will watch what they do with interest.

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"I liked watching some of the younger players, like Barrie McKay, who scored a fantastic goal. Players like him, they have real potential. When you speak about them after such a game, you can’t say whether they will play like that for a whole season. They still have to become real top-league players.

"Doing that many seasons in a row is very different from having one or two very good games. But I think that some of them definitely have the potential and this should prove to them that they can do it."

Le Guen was given a warm welcome by Rangers supporters outside of the stadium and he said: "I look back on my time at Rangers with only good memories. That is why I wanted to come back.

"First of all, you have a beautiful country. But I also had a good experience. I want to keep in my mind only good memories. That is the best way to go through life."

READ MORE: Rangers will receive funds needed to challenge Celtic, says vice-chairman Paul Murray