The 21-year-old suffered the injury during an FA Cup tie against Chesterfield in December 2012 and he was initially ruled out for six weeks, but his comeback has been continually put back.
Wallace has been told by specialists that his knee is healing well, but he could be out of action for a further two months.
"There were [doubts] in my head but the people around me didn't think that," Wallace told BBC Radio Merseyside.
"When you're getting setback after setback, there were times where I was very negative and I thought it wasn't going to get any better.
"This has been the hardest time of my career. I've never had this problem before with an injury for this long. It's been tough on me, and luckily I've had good people around me supporting me and keeping my head up. I thank them a lot for what they've done for me."
Wallace joined the Prenton Park club from Everton in 2012.