Antoine Griezmann
Antoine Griezmann has hugely impressed at Sociedad this season. [Twitter]

Manchester United are set to spend big this month and reports suggest Davis Moyes sent his chief scout Robbie Cooke to Spain last weekend to watch some of the stars of La Liga who could strengthen the struggling Premier League champions – including Diego Costa, Koke, Ander Herrera, Antoine Griezmann and Iñigo Martínez.

United's latest defeat against Swansea in the FA Cup and against Tottenham on New Year's Day in the Premier League have increased the club's urgency to make several signings this month.

The Daily Mail reported that Cooke was watching Diego Costa, Koke and Ander Herrera but the Spanish press have added some other names that could be tempted to move to Old Trafford during this January transfer window.

Reports suggest Cooke, who worked alongside Moyes at Everton, was at the La Rosaleda stadium on Saturday, where Atletico beat Malaga 1-0 thanks to a goal from Koke. The United scout was also present at Anoeta on Sunday to see Real Sociedad beat over Athletic, where Griezmann scored with a magnificent individual effort.

Diego Costa

Costa is the joint top scorer in La Liga this season, ahead of Cristiano Ronaldo, after scored 19 goals in just 20 games and he has caught the eye of Liverpool, Arsenal and Manchester United.

The 25 year-old striker has a contract at the Vicente Calderon until the summer of 2018 but his release clause is just £31m.

Costa is happy at Atletico Madrid but his club have sold other stars in the past such as Sergio Aguero and Radamel Falcao due to economic issues.

Koke

Koke is the other key player behind Atletico Madrid's amazing start to the season. He would fit into Moyes' squad perfectly as he can play in the centre of midfield as well as a playmaker.

The 21-year-old midfielder is second in the assists rankings in La Liga, just behind Cesc Fabregas, and Liverpool have also been linked with a move.

Nevertheless, his agent has insisted several times that Koke wants to stay at the Vicente Calderon and indeed last summer he signed a new contract with Atletico, extending his stay until 2018 and getting a significant pay rise.

Ander Herrera

United tried to sign Herrera last summer but the club finally refused to meet his £36m release clause and decided instead to sign Marouane Fellaini.

However, Moyes may yet go back with a renewed attempt to sign the 24-year-old playmaker who is becoming a key player for Athletic Bilbao after a slow start to the season.

The Spaniard has insisted in public that there is no chance of a move to United in January but if he was close last summer to a move then those at Old Trafford may believe that there is still a chance to sign him.

Antoine Griezmann

The 22-year-old winger has enjoyed a wonderful start to the season, scoring 12 goals in just 16 La Liga games. He has netted more goals than Lionel Messi and he is just behind Cristiano Ronaldo, Diego Costa and Javi Guerra despite not being a striker.

Tottenham tried to sign him last summer and Arsenal have also been linked recently with a move. In Spain reports suggest that Real Sociedad are willing to sell him next summer for around £30m (his release clause is £36m) but it looks unlikely that they accept offers during this transfer window.

Iñigo Martínez

With Rio Ferdinand's contract expiring at the end of the season, David Moyes is looking for a centre-back and Martínez is one of the best talents in La Liga.

He is strong and technically superb with the ball but some questions have been asked of his lack of speed. His release clause is £30m but Real Sociedad could be open to accept lower offers for him.