It appears the Netherlands-based defender will be ruled out of next month's FIFA World Cup qualifiers against Bangladesh and Tajikistan.
Sainsbury, an imposing and impressive ever-present in the Socceroos' run to glory at January’s AFC Asian Cup, was aiming to be back in the frame for the games in Perth on 3 September, and in Tajikistan five days later.
Sainsbury missed June’s opening qualifier against Kyrgyzstan in Bishkek with injury, and the same hamstring problem has flared again, this time in his other leg.
As a result, the 23-year-old is at long odds to prove his fitness for his club PEC Zwolle over the next two rounds of the Eredivisie, let alone for his country. He missed the opening two games of the season, a 2-2 draw against Cambuur and a 3-0 win over De Graafschap.
“My left hamstring is fine now but there’s been a problem with the other one,” Sainsbury said.
“It’s frustrating but at the same time I have to do what’s best for me, and make sure I play a lot more games in the future rather than just trying to bang out a few now."
“I’m not too focused on that (Socceroos selection) right now. I am working on getting a few games for my club first and we’ll see what happens after that.
“At the end of the day, it’s not the worst thing in the world to miss these games, although of course it’s not ideal.
“I wish the boys all the best and hopefully they will take maximum points. Obviously if I am not in the squad I would be devastated but I also have to get myself right for the games after that.”
Sainsbury, who picked up his last cap for his country in March's 0-0 draw against Macedonia in Skopje, is slated to return to training on Monday.
He has been undergoing an intensive regime to overcome the hamstring issues, but refused to blame the injuries on the artificial surface he trains on and plays on at club level.
“I’ve been working on my hamstrings, glutes, core and trunk to be able to handle the load of European football," Sainsbury said.
“I usually say to people if you train and play on an artificial pitch you have to expect at least one injury within the first three weeks, because your body is not used to it.
“But after that you just carry on and forget about the surface.”
The defender, who joined from the Central Coast Mariners in January last year, is entering the final year of his contract.
Sainsbury knows an impressive season is paramount, because he wants to take the next step in his career and move on to pastures new.
"I need to have a good year and to put in a big shift, if I do that hopefully I will be in a position to move on to bigger and better things," he said.
“I would like to progress my career at a bigger club in a bigger league. But I am not making any assumptions. I need to start playing some games first.
“I’d love to have a crack at the Premier League, but at the same time I have to ready mentally and physically and have a full season in Holland first and see where that can take me. I am open to anything really.”
"Holland has made me a better player overall and for Australia Ange Postecoglou has put the pressure on, which makes you perform.
"He has a presence about him which makes you want to give our all for your country.”
PEC Zwolle surprised everyone last season. It beat Ajax in both the KNVB Cup and Dutch Supercup, but this season looks like it will be a tougher task.
Sainsbury was circumspect about his side's chances of causing a stir this time around.
“Everybody has written us off a little bit at the moment and are expecting us to finish 12th or 13th,” he said.
“We are a very young and inexperienced squad, but are only going to get better as the season goes on.
“We lost several players who were the spine of the team but we are happy with the players who have been brought in.”
