Juventus midfielder took to Twitter to express his surprise at reports suggesting he aggravated his knee while on international duty.
Reports in the summer suggested Manchester United Louis van Gaal decided against making a move for the midfielder during the transfer window because of on going knee problems.
But the 27-year-old was quick to rubbish stories: "My knee is perfect," the Chile international wrote on Twitter.
"Please stop inventing stories and get your facts straight. Let's go Chile!"
The Chilean featured for Juventus in their debut game against Chievo in the Italian Serie A and is expected to start at home against Udinese after the international break.
