The former Manchester United manager was dumped less than a month into the new Bundesliga season - Bayer management later conceding they were second-guessing their decision to appoint the Dutchman after just a few weeks into the summer's preseason.
Helmer told Tribalfootball.com: "It's crazy. They probably felt the same after two games. Or three competitive games, let's say.
"There was a national game, but that so much went wrong internally, so much against him. Apparently they had no idea that the coach had no way of reaching (forming a relationship with) the team.
"I don't know how the team reacted internally, but it's been a big change. Many players are gone, many important players, and then new ones have come in.
"As a coach, you always have to try to bring them all under one roof. Apparently he didn't manage to do that, and I found that more than surprising. (A situation that) really was not good for him, I would say."
Ten Hag has since been replaced by former Denmark coach Kasper Hjulmand, a decision Helmer admits could be risky by Bayer's board.
He added, "I don't know, but he's making a good impression on me. I don't think it's a technical problem. He has a whole new team to find out about, and as I said, he's lost a lot of important players.
"The question is how quickly he can create a successful team again... ?"
Xhaka choice
Helmer had a short spell at Sunderland in the latter stages of his career and admits he was surprised by Granit Xhaka's decision to leave Bayer for the Black Cats last month.
He also said: "Yes, it's not just about money with Xhaka. You have to convince him. From the sportsman, from the other side, where do you want to go with the team and so on.
"That really surprised me. It was relatively clear that they would do it, that they would talk to each other and then they convinced him relatively quickly. He wanted to go there too. They did a good job."
- Thomas Helmer was speaking to Tribalfootball on behalf of Coin Poker