The 24-year-old has recently stepped up his comeback with some light training and believes he will be ready to resume full training in the New Year.
"I've been injured since May and when you can't do what you're paid to do it's massively frustrating," he told the club's official website.
"I had a lot of expectations surrounding this season and what it might hold for me but I have to put those aside for now.
"When you're told you're going to be out for eight months and no sooner you just have to knuckle down and get on with it.
"Earlier this month, I started doing a few things - just having someone hit volleys into my hands. But I'll start doing some proper sessions soon with the goalkeeper coach and that will push the knee a bit further.
"The aim at the moment is to be doing full training and getting involved with the lads sometime after Christmas - probably early February."
Meanwhile Foster, who spent the last two seasons on loan at Watford, has not ruled out the prospect of leaving Old Trafford again on a short-term basis in a bid to rediscover his match fitness.
He added: "I can't wait until I'm playing again. I guess that might be around March next year.
"It's something to look forward to and something to aim for. Whether it's at United in the reserves or somewhere else on loan, I'm not bothered ? I'll take anything!"