Aberdeen were thrashed 5-1 at home by Sigma Olomouc on Thursday
Tony Mowbray and Craig Levein have rejected the idea that summer football would have prevented this week's poor Scottish results in Europe.
Scottish FA chief executive Gordon Smith suggested that moving the fixtures could help clubs compete.
But Dundee United boss Levein thought defeats for Aberdeen, Celtic and Motherwell were more down to them having new managers in charge.
Celtic's Mowbray thought the financial strength of clubs was the main factor.
Mowbray's team lost 1-0 at home to Dinamo Moscow in his first competitive game as Celtic manager on Wednesday.
That Champions League qualifier was followed by Aberdeen being hammered 5-1 at home to Sigma Olomouc and Motherwell losing 3-0 to Steaua Bucharest, both in Europa League qualifying.
Falkirk's first foray into European competition had previously ended with an extra-time defeat by Liechtenstein club Vaduz, who had been relegated from the Swiss top-flight.
For me, it isn't insignificant that each of the teams has had a new manager in the summer
Dundee United manager Craig Levein
But Mowbray said: "I don't think it was a fitness issue the other night. We just played against a very good team.
"Three days earlier, we had beaten Tottenham Hotspur, who have aspirations of breaking into the top six in England, with what was basically a reserve side, and we beat the African champions 5-0.
"Fundamentally, Scottish football is lacking the funds of some of the teams in European football.
"Football is usually about resources. We played a Russian team which is awash with money from a league that is awash with money, as are some of the other leagues around Europe, like in England.
"Unfortunately, the Scottish game at this moment doesn't attract the sponsorship or the money to bring better quality footballers to help the teams compete better."
Levein pointed out that the three teams suffering defeat this week - and Falkirk a week earlier - had new managers in charge.
"For me, it isn't insignificant that each of the teams has had a new manager in the summer," he told BBC Scotland.
"It's hard enough going into Europe when you know your players and you know exactly what they're capable of.
Mowbray not in favour of summer games
"If any of those managers were playing against an SPL side then, apart from Jim Gannon at Motherwell, they'd have a better idea of what they're facing.
"But, when you're facing foreign opposition, the last thing you want is to be unsure of what you have as a manager."
Levein thought that the Scots were too quick to criticise their teams and players.
"Again, we're away down this doom and gloom route," he said. "I think the teams are a little bit better than what they showed.
"I do think that the fact that each club had a new manager in place in the summer, hadn't had time to work on the players, didn't know the players, these things make a hell of a difference."
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