The young defender fell awkwardly on his knee after an aerial challenge in our Premiership finale against Manchester United on Saturday.
It was initially thought he had just jarred his right knee but scans on Monday showed serious damage to his medial ligament.
He has been told by specialists that it could be up to three months before he can start training again - ruling him out of this week's England Under-21 action, the start of pre-season and the start of next season's Premiership campaign on August 18. In fact, if the worst comes to the worst, he may not start training again until the end of August.
It is a huge setback for the 20-year-old who burst onto the Premiership scene with an extended run in the first team towards the end of the season.
Naturally downbeat, Anthony said: "I’ve a lot of damage in my ligaments on my left knee.
"At first I just thought I’d twisted it or jarred it and even in the dressing room afterwards it was in my head that I’d just twisted but I had the scan on Monday and it was a bit worse than expected.
"The last thing I needed was to get an injury at the end of the season and have to fight my way to fitness again before getting back into the frame."
We will print Anthony's full reaction, with audio, on the site tomorrow.
Anthony Gardner faces a three-month stint on the sidelines after scans revealed the true extent of his knee injury.