Pearson, who has gone back after spending two years at Championship team Derby County, told BBC radio: "Phil will be manager on Sunday but there's no point me saying he's got a job for life, that's not the case.
"We need results quickly and that puts pressure on everyone at the club."
Hull are third from bottom but have won only three league matches in 2009.
Pearson added: "How secure is the manager? That's a tricky one. I think if we don't get results then that security goes down.
"Phil knows that. It's the business we're in. It's been a difficult year and we need to achieve results quickly. We'll have to see what happens over the next couple of weeks."
Last week auditors Deloitte said Hull needed 23 million pounds to meet existing liabilities and that relegation would be a major blow to their finances, according to media reports.
"The club is trading and is solvent and it can be sorted out but there are too many costs surrounding it which seem to have become a little superfluous," added Pearson while indicating the wage bill was too high.
"What's the phrase? Maybe a little too much champagne, maybe not enough ale."
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