Manchester United's summer target Arturo Vidal has aggravated his troublesome knee whilst on international duty for Chile.

The Juventus star had to quit a routine training session in Miami, where Chile face Mexico and Haiti in friendlies, but is set to have a series of tests before returning to Italy.

Vidal was heavily linked with a move to Old Trafford throughout the summer, but nothing materialised despite a series of negotiations between the clubs.

VIDEO Scroll down for Massimiliano Allegri: Vidal happy to stay at Juventus

Opening win: Arturo Vidal featured in Juventus' 1-0 win at Chievo in Serie A before the international break

The 27-year-old required knee surgery towards the end of last season and was evidently far from fully fit at the World Cup.

Manchester United manager Louis van Gaal is an admirer of Vidal but was hesitant to fork out a significant fee, with question marks surrounding the player's fitness.

Instead, United paid a British record fee of £60million for Angel di Maria.

These concerns could be justified as Vidal might have to go back for more surgery in an attempt to alleviate the niggling problem. If so, the Chilean will be on the sidelines for a considerable amount of time.

New Juventus manager Massimiliano Allegri will be frustrated by the revelations as he is trying to cope without talismanic playmaker Andrea Pirlo, who is out until October.

Midfield force: The Chile midfielder was a top summer transfer target of Manchester United

Passionate: Vidal played with plenty of endeavour at the World Cup but lacked full fitness after knee surgery

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