It could be a lucrative transfer window for Celtic this summer, with the Parkhead club in line to significantly bolster their kitty without having to lift a finger.

Clauses in the contracts of Victor Wanyama, Fraser Forster and Virgil van Dijk could all mean a summer with a surprise bonus if any of the trio move on from Southampton.

Wanyama is the most likely, with Tottenham Hotspur believed to be leading the race for the Kenyan internationalist.

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Spurs boss Mauricio Pochettino was rebuffed last summer when he tried to sign Wanyama in an attempt to strengthen his central midfield. With Champions League football assured for the London side this season, the 24-year-old Wanyama is seen as an ideal acquisition.Glasgow Times:

And that could net Celtic anything up to £4m, with the club’s sell-on fee believed to be as high as 20%.

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With Wanyama going into the final 12 months of his contract, it makes sense for Southampton to cash in on him in the current window.

Van Dijk’s situation is not quite so lucrative, but could still gift Celtic a tidy sum. The Parkhead side paid out just under £1m to Groningen when the defender moved to Southampton last August in a deal that was worth almost £13m to Celtic.

The player signed a whopping six-year deal at St Mary's only last month after an impressive maiden season with the Premiership side but it is believed he is high on the wanted list of Ronald Koeman, the new Everton manager, who has been promised significant funds this summer.

Glasgow Times: Southampton manager Ronald Koeman has reiterated that Victor Wanyama will not be sold before Tuesday's deadline

It is believed the deal to take Koeman to Goodison was held up because of Southampton, where he is going from, wanted a clause inserted to prevent him from plundering their players. Everton stood firm in their refusal and it is believed that Van Dijk will be pursued now by the Everton manager.

Forster, too, as back-up England keeper could also find himself in line for a switch.

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Veteran keeper Tim Howard's time at the club has come to an end and Forster is being lined up as the man to take the place between the sticks in Liverpool for the new season, which would lead to another pay-out for Celtic.

The Parkhead side sold Forster to Southampton for £10m in 2014, although they had to pay a percentage of that fee to Newcastle where they had originally take the keeper in loan from before making the deal permanent.

A sell-on clause of 10% is believed to be included in the deal which would be a welcome bonus for Brendan Rodgers as he sets about rebuilding the current squad.