The Royals parted company with the 51-year-old on Monday, with the club sitting four points from safety in the Premier League table and staring at the prospect of relegation following four consecutive defeats.
His firing shocked some people after he had guided Reading to promotion last season, and Villas-Boas compared it to the dismissal of Nigel Adkins from Southampton earlier in the campaign.
"Extremely disappointing. I think it was along the same lines as what happened to Nigel at Southampton," Villas-Boas told Sky Sports News.
"I think sometimes you are a victim of the success that you have achieved. You do ever so well to put clubs in the Premier League and then you pay the price when probably given the best conditions to succeed.
"I think it's tremendously unfair. Obviously it's not my decision, or my responsibility, it's something that happens in the game. It happened to me before. I just hope that Brian is able to continue showing his qualities because it was his quality that put Reading in the Premier League."
McDermott took charge of Reading in 2009.