Having been sacked as Birmingham City manager in early January after just two wins in 15 games, the pressure was on Rooney to show he can repeat the career he had as a player as a coach.
His side struggled to defend against a Sheffield Wednesday side that seemed to be able to attack at will.
Having already signed six players this season Rooney says he is open to adding to his squad but will not panic after their opening day drubbing.
“It’s the first game of the season and of course we’re disappointed,” Rooney said.
“But I don’t think it’s time to panic, I’ve seen the work we’ve done throughout the pre-season which gives me encouragement.
“If players become available who we feel can improve the team then of course we’ll look at that, but I don’t think we can start panic buying after one game.”
Rooney started Conor Hazard in goal with continued speculation linking popular homegrown goalkeeper Michael Cooper with a move away from the club.
The 24-year-old in in the final year of his contract and has rejected the offer of a new deal at Home Park.
“There’s a lot of speculation. I’m sure he’s aware of what’s happening and the bids we’re receiving and so I need players who are fully motivated and committed to play,” Rooney said.
When asked if Cooper will still be at Argyle after the transfer window he said: “I’ve no idea.
“I think as a football club we do need to make a decision and obviously the bids we’ve received are not the valuation.
“I think it’s really important for me to say I really want Michael to stay, I think he’s a fantastic goalkeeper.
“But I think sometimes it gets taken out of the manager’s hands as well in terms of what conversations have been had with Michael and the club.”