Alex Neil felt Norwich City failed to "get their fair share of the decisions" during the 3-0 home loss to Tottenham on Tuesday.
Dele Alli gave the visitors the perfect start with a goal inside two minutes, while he was also heavily involved in Tottenham's second.
The midfielder was adjudged to have been fouled inside the area by Norwich defender Sebastien Bassong, although Neil felt the decision by referee Kevin Friend to point to the spot was harsh.
Steven Naismith was also denied a spot kick at the other end of the field after a clumsy challenge by Kevin Wimmer.
"Once you concede in the first minute and a half, we make it difficult for ourselves," Neil told the club's official website.
"The penalty is the softest penalty I've seen all season. We didn't get the fair share of the decisions and that cost us.
"If it was a clear penalty, I'd be the first to hold my hands up."
Neil admitted his squad must put the home defeat behind them ahead of a crucial trip to bottom club Aston Villa on Saturday.
"The next game becomes huge for us now," he added.
"The Villa game was always a big game though. We've got important matches coming up and we need to pick up points."
