Striker Sam Cosgrove has left Carlisle United and joined Scottish Premiership side Aberdeen for a fee believed to be in the region of £40,000.

The 21-year-old striker sealed a two-and-a-half year deal with the Pittodrie outfit.

And it emerged that the frontman had already signed a pre-contract agreement to join the Dons in the summer - leading United to negotiate a quicker departure.

United claimed Cosgrove's head had been turned by Aberdeen's interest and also said it was in Carlisle's financial interests for him to leave now rather than the club wait until the end of his contract.

The fee was officially undisclosed but the News & Star understands it is around the £40,000 mark.

In a statement on the United website, chief executive Nigel Clibbens said the striker had made it clear he saw his future north of the border.

"From Keith’s conversations with Sam, and with his agent, it was made very clear that there was absolutely no prospect of Sam staying beyond 30 June 2018," Clibbens said.

"That tells us that he had his head ‘turned’ by the prospect of playing in the SPL which, obviously, includes games against the Old Firm and a number of other very good Scottish clubs, and also in Europe.

"His strong preference was for a clean break now. We talked about extending Sam’s deal, but it was made clear that the situation had come around based on the opportunity he had been presented for a move to the SPL with Aberdeen. Therefore, a new contract was not an option either.

"Faced with that inevitability we had two choices. Firstly, we could have continued with Sam as part of the Carlisle United squad for the rest of his time here [but] he would have been doing this with team mates, coaching staff and fans knowing his future and commitment was elsewhere.

"We would then receive the prescribed training compensation applicable when he moved on to join Aberdeen.

"The alternative was to reach agreement for him to go now.

"As an under-24 player, Sam would also be moving across an international border. Therefore, the compensation we are due is a small, fixed sum for every year he has been with Carlisle United - that’s it.

"By the end of his contract, Sam would have been here for approximately 11 months. That also severely limits the fixed payment we would get.”

"With that in mind, we knew we had to consider all options and find the best outcome for the club and for the player.

"Having carefully considered the pros and cons, we reluctantly decided to agree to a transfer deal being done now. On footballing grounds, we need everyone to be focused on the games ahead and not to be looking elsewhere.

"The situation is not one we wanted, but we have sought to make the best from what we’re faced with."

Cosgrove, 21, scored once in his six starts and six substitute appearances for the Blues.

He initially made the move to Cumbria on a short-term deal in the summer before then signing a second deal until the end of the season.

"Sam was keen to make the move to the SPL and, having made sure we got the best outcome for all parties, we wish him well as he now joins Aberdeen," manager Keith Curle added.

Aberdeen boss Derek McInnes said: "Sam was one we had earmarked for the summer but during conversations with Carlisle it became clear they were keen to agree a deal for Sam in this transfer window, so things progressed quickly.

"He's a young guy who we feel has lots of potential and we're looking forward to working with him to further develop his talent."