Rafa Benitez could leave Newcastle before Christmas as he is frustrated by transfer inactivity, insists Alan Shearer

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Alan Shearer has thrown serious doubt over Rafa Benitez's future at Newcastle by insisting there's no guarantee the Spaniard will still be there at Christmas. 

Benitez, who helped Newcastle secure promotion back to the top flight at the first time of asking, has grown frustrated at the club's lack of transfers. 

Newcastle have made five first-team signings with Florian Lejeune, Jacob Murphy, Javier Manquillo and Mikel Merino joining the club.

Alan Shearer believes Rafa Benitez may not be Newcastle manager at Christmas

The Spanish tactician is frustrated by Newcastle's lack of summer transfer business

Benitez has also been able to turn Christian Atsu's loan move into a permanent deal but the former Liverpool and Chelsea manager is not content with his side's summer business. 

And club legend Shearer has told the club's supporters that all is not well at the Toon Army ahead of their Premier League opener with Tottenham on Sunday. 

Shearer, speaking to talkSPORT, said: 'I don't think we can guarantee that [he stays]. I think there's definitely a frustration there from him, having spoken to him.

'They've been in for a lot of players and they've missed out on a lot of players.

'They have tried, but for different reasons they haven't got some of the players in that they've wanted. They've been too late, other clubs have gone ahead and beaten them to it.

'Rafa will have them hard to beat, he'll have them organised and well-drilled, but Rafa wants to be bigger and better than that. 

'He will have to have signs of bringing more players in, and I think it's a big two or three weeks regarding bringing a few more in. He needs that, there's no doubt about it. 

'I think we'll know a lot in a month's time and if he doesn't get what he wants than you might see it starting to unravel.' 

Shearer went on to post a picture of himself in conversation with Benitez alongside the caption: 'I sensed a little frustration from Rafa when I spoke to him at the Premier League launch today.' 

Jacob Murphy was Benitez's third transfer arriving from Norwich for £12million in July 

Newcastle won the Championship last season and return to the Premier League on Sunday