The Portuguese captain claimed the pools were old and a health hazard.
Cristiano Ronaldo reportedly forced a number of changes at Manchester United's training ground after complaining about the state of its swimming pool on his return to the club.
The 37-year-old re-signed for the Red Devils last summer and has experienced a largely successful individual campaign on his Old Trafford comeback.
However, the Portuguese international is said to have been shocked by the state of United's training facilities at Carrington.
Ronaldo claimed swimming pool was a 'health hazard'
As reported by The Mirror, Ronaldo believed that no upgrades had been made since he left for Real Madrid in 2009, with his main gripe being with the standard of the swimming pools at the training ground.
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The report claims that the five-time Ballon d'Or winner complained that "loose, chipped and missing tiles" within the pools were a safety hazard - and as a result, refused to use them.
Ronaldo made sure that he had an indoor pool at his home so that he could still perform water-based drills away from the training complex.
It is thought that the Red Devils have taken the forward's criticism onboard and have ordered work to be completed on the pools in order to get them ready for pre-season.
United have also spent £200,000 on a new boiler system, with their old one reportedly causing issues with hot and cold water during the winter months.
Red Devils to continue training ground facelift.
Man United - who moved to Carrington from The Cliff in 2000 - are keen to improve their training ground by erecting new floodlights and a 500-seater stand.
Chief Operating Officer Collette Roche said last year: "Longer term, we are looking at fuller redevelopment plans for Carrington to ensure it will be a state-of-the-art, fully integrated facility for our men’s, women’s and academy groups.
"Significant, game-changing investment will be made into our training facilities to take Carrington to the next level once again."
Ronaldo registered 24 goals and three assists in 38 appearances for the Red Devils this season, helping the club to sixth position in the Premier League.
