Celtic legend Peter Grant reckons Mo Johnston's infamous switch from Parkhead to Rangers caused 'nine years of torture' for the Hoops. 

Perhaps the most high-profile and talked about signing in the history of Scottish football, Johnston penned a deal at Ibrox in 1989 - two years after leaving fierce rivals Celtic for Nantes.

The hit man was set to re-sign for Celts but opted to join Rangers under Graeme Souness at the eleventh hour.

And Former Celtic captain Grant recalled the moment he first heard from Johnston and his soon-to-be strike partner Ally McCoist that he'd changed allegiances - as they were all away on Scotland duty.

Speaking on Si Ferry's Open Goal show, Grant said: "The first warning sign was the cup final.

"We beat Rangers and we'd signed Mo but it didn't go through.

"Mo travelled on the bus with us to the game. He said 'everything's done, just not signed the paperwork'.

"I didn't think any more of it, he'd got his pictures done, he was going down as a Celtic player, really, to the cup final.

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"After the cup final I was with the Scotland squad for the Rous Cup against England in Chile.

"We were at Turnberry and I seen big Billy [McNeill] storming away. He was down to see Mo.

"We're going to train and Coisty and Mo are on the bus and Coisty goes 'me and the wee man are going to terrorise you next year, Granty'.

"I laughed and said 'I know we are, Coisty'. He went 'naw, Granty, I'm going to sign for Rangers'. I thought 'away you go', I still didn't believe him.

"Then the next thing he's announced he's going to be a Rangers player. It should never have been allowed to happen.

"That was, for me, what cost the next nine years of torture for Celtic, that moment. 100 per cent."

Grant remains adamant that Johnston's move to Rangers should never have been allowed as the beaks at Parkhead should have pushed the boat out to give the striker "whatever he wanted".

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And in the end, Grant reckons it cost them and was the main reason Celts endured so much "torture".

He added: "Mo Johnston should never have been let go to Rangers, anybody else it can happen, not Rangers.

"Celtic player who's a Celtic player should never have went to or been allowed to go to Rangers.

"Celtic should've given everything to him, no matter what he wanted. That's what cost Celtic the next nine years.

"On the pitch I kicked him a few times but didn't meet him fully face to face until Canada."