Aberdeen have suffered a double blow in central defence after Ash Taylor's relapse followed Scott McKenna's hamstring injury.
McKenna has been ruled out for several weeks after being left out of the Scotland squad following his injury against Kilmarnock last weekend.
And Taylor has experienced a major setback in his comeback from the hamstring injury he suffered against Chikhura Sachkhere on July 25.
Mikey Devlin is now in line to make his comeback against Ross County at Pittodrie on Saturday following more than six weeks on the sidelines with his own hamstring problem.
McInnes said: "Scott got his scan results and will be out with a tear as expected, probably in the region three to four weeks. Maybe a bit longer than that, maybe a bit quicker, he has been a quick healer in the past.
"Any team in Scotland would miss a player of Scott McKenna's ability.
"It's a double whammy for him as he misses out international-wise as well.
"He was in good form, there has been a lot documented and his situation over the last wee while but he has dealt with it and been very important for us. His level of performance has been very strong.
"We missed him a couple of times last season with hamstring injuries and we will have to do without him again this time round."
On Taylor, McInnes said: "He had a bit of a relapse on Tuesday to the injury just as he was getting to the final stages of that, which is the worst news possible for him and for us, after doing all the rehab and putting all the work in. He was due to return to training on Thursday, today.
"I don't think it's a small setback. He is away to get scanned and we will find out but we feel he will be out for another few weeks yet."
"So with that in mind, we restricted Mikey Devlin's game time on Tuesday in the reserves to 45 minutes because we don't want to put any more at risk."
