It was Leinster's second defeat in their three Magners League games to date and the disappointing start by their own incredibly high standards has put Schmidt under early pressure from the media.
But Costello has insisted Schmidt is not to blame for the losses, stating that the New Zealander needs time to settle in.
"Any new coach takes a while to bed in," Costello told The Irish Independent.
"He needs to get to know his players, read their body language, find out what they like to do, what areas they like to be in.
"Don't forget he coached Clermont against Leinster last year in the Heineken Cup and he could have had certain ideas about the strengths and weakness of Leinster and he could have been wrong. So, he'll have his ideas. It will take a while to sort it all out.
"Winning obviously helps a lot in this situation and it's been a tough start to the season, particularly going down in Treviso, but not having the likes of Brian (O'Driscoll) and Jamie (Heaslip) and Leo (Cullen) is hugely significant because they are the backbone of the team.
"It takes a while to sort these things out. I like to think the bedding-in period is around three months, particularly with top players coming back in at different times.
"So I wouldn't be in any way saying Leinster are anywhere near a crisis. Leinster are old enough and experienced enough to look at the bigger picture, but they do need to get back to winning ways as soon as possible."
Leinster's next chance to do just that comes at Murrayfield this Friday when they face an Edinburgh side looking for their first win of the season.
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