Newcastle United manager Rafael Benitez has reiterated his frustration at not being able to bolster his squad adequately, claiming he is "not happy" about the club's summer business so far.

The Spaniard steered the Magpies back to the Premier League at the first time of asking last season and has already made six signings this summer, including Jacob Murphy from Norwich City for £12m (€13.3m, $15.6m) and Florian Lejeune from Eibar for £8.7m.

However, the former Liverpool, Chelsea and Real Madrid manager insisted Newcastle, who begin the Premier League campaign against Tottenham Hotspur on Sunday (13 August), have not strengthened enough.

"I am not happy [with transfer dealings] but for me it is a challenge," he told Sky Sports.

"I want to do my best. Every manager wants to improve and have better players, but at the same time, I am happy with the players I have because the team spirit was good last season and hopefully we can replicate that.

"It is important for the fans to understand that this year will be totally different. For the players it must be the same. We must have a game plan and try and stick to it."

The Magpies had kept tabs former Manchester City goalkeeper Willy Caballero and Chelsea forward Tammy Abraham, but the former moved to Stamford Bridge as a free agent, while the latter opted to join Swansea City on loan.

"We missed some targets at the beginning and we're paying for that," the Spaniard added. "Hopefully we can find solutions and bring what we need. It's not what you want, it's what you need.''

Newcastle owner Mike Ashley promised to invest "every penny" gained from promotion in the first team after the Toon Army won the Championship last season but Benitez, who has repeatedly underlined the need to bolster his squad, admitted signing players has become increasingly difficult because of the inflated transfer fees that have become routine in the Premier League.

"Sometimes it is not about you want, it is about what you need and what you can afford now," he said. "It is hard for teams who don't have as much money as the big teams. Average players now cost big money. Everything is a little more difficult. We have to be sure the player is good enough for what we are looking for."

Earlier this week, the 57-year-old confirmed his interest in signing Lucas Perez from Arsenal as the Spaniard looks set to leave north London after the arrival of Alexandre Lacazette.

However, Deportivo La Coruna are also keen on re-signing the 28-year-old who started just two Premier League matches last term.

Newcastle's all-time leading goalscorer Alan Shearer shared Benitez's concerns but remained confident the Spaniard's tactical nous would offset any personnel deficiencies.

"It has been a frustrating summer for him [Benitez]," Shearer said. "At the end of last season, Mike Ashley said he would give every penny he had to Rafa. I don't know if that has been the case. But with his experience and know-how, he will set the team up to be very difficult to beat."

Rafael Benitez
Benitez remains hopeful of making further signings. Reuters