Liverpool boss Juergen Klopp called it "not a good day for football" while Jose Mourinho labelled it as a "disgraceful decision" as Manchester City had their European ban in the Court of Arbitration for Sport (CAS) on Monday.
On Monday, City won their appeal against the two-year ban from UEFA competition in CAS, meaning they will be allowed to participate in next season's Champions League.
CAS ruled that City had not broken the Financial Fair Play (FFP) rules by disguising equity funding as sponsorship. However, City were fined 10 million euros ($11.37 million) for failing to cooperate with European soccer's governing body.
Mourinho was left unhappy because he felt the decision was contradictory as it should have either been a ban for the breach or nothing at all for being innocent but the fine and no ban didn't go down well with him.
"In any case it's a disgraceful decision because if City are not guilty then they should not be punished with the fine," Mourinho told reporters in a virtual news conference ahead of Wednesday's clash against 13th-placed Newcastle United.
"If you're not guilty you shouldn't have a fine. If they are guilty the decision is also a disgrace and they should be banned from the competition. I don't know if City are guilty or not but either way it's a disgraceful decision."
Klopp, on the other hand, felt the current FFP framework was not somewhat that they should be sticking to.
"I don't think it was a good day for football yesterday, to be honest," Klopp told a virtual news conference on Tuesday.
"FFP is a good idea. It is there for protecting teams and the competition, so that nobody overspends and have to make sure the money they want to spend is based on the right sources.
"It's not up to me to judge this and I don't but I think this FFP framework we should stick to. I hope FFP stays just because it gives kind of borders that you can go to, but not over it, and that's good for football," Klopp said.
"If you start doing that nobody has to care any more and the richest people or countries can do what they want.
"It will make the competition really difficult and I think that would lead automatically to a kind of world super league with like 10 clubs and it would depend on who owns the clubs and not the names of the clubs. It makes sense to have these rules."
Klopp did say, however, that City's place in the Champions League next season might at least benefit Liverpool as they try to retain their Premier League title.
"They won't have 10 or 12 games less now -- no other team would have had a chance in the (Premier) league," he said.
UEFA's FFP rules face likely changes in the wake of the CAS ruling and Mourinho said the system needs to be overhauled if it is to continue to serve its purpose which is to aim to stop clubs running big losses through spending on players.
"I think this is going to be the end of Financial Fair Play because there is no point," Mourinho said. "I would like to see it used in a proper way. At this moment we are talking about Man City but in the past other clubs were in a similar situation.
"I think it's better to open the circus door and let everybody enjoy."
(With Reuters inputs)