After being sacked as manager of Birmingham City in early January after just two wins in 15 games, Rooney was under pressure to show that he could replicate his career as a player as a manager.
His team struggled to defend against a Sheffield Wednesday side that seemed to be able to attack at will.
Rooney has already signed six players this season and says he is open to strengthening his squad. However, he is not panicking after the defeat on the first matchday.
“It’s the first game of the season and of course we’re disappointed,” said Rooney.
“But I don’t think it’s time to panic. I’ve seen the work we’ve done throughout the preseason and that gives me courage.
“If players become available who we believe can strengthen the team, we will of course look at that. But I don’t think we can start panic buying after one game.”
Rooney left Conor Hazard starting in goal and there was ongoing speculation that popular homegrown goalkeeper Michael Cooper could leave the club.
The 24-year-old is in the final year of his contract and has rejected the offer of a new deal at Home Park.
“There is a lot of speculation. I am sure he knows what is happening and what offers we are receiving. That is why I need players who are fully motivated and ready to play,” said Rooney.
When asked if Cooper would still be at Argyle after the transfer window, he said: “I have no idea.
“I think as a football club we have to make a decision and of course the offers we have received do not reflect the valuation.
“I think it’s really important for me to say that I really want Michael to stay. I think he’s a fantastic goalkeeper.
“But I think sometimes the manager is also deprived of control over what discussions have been held with Michael and the club.”
