After a dismal end to the 2014/15 campaign, hopes were raised on Tyneside following the big-money signings of Georginio Wijnaldum, Aleksandar Mitrovic and Chancel Mbemba.
However, after a disappointing 2-0 defeat to Swansea on Saturday, McClaren admits the club could delve back into the transfer market – with Marseille’s Florian Thauvin reportedly close to a move to St James’ Park.
“We’ve never finished until the window closes. Who knows? At the moment we’ve just signed three so we’ve settled down,” he said.
“We then need to look at the first few games. Unfortunately, I’ve learnt nothing (against Swansea).
“Any good manager will tell you he’s always looking for players. We’d love one or two more but they’ve got to be the right ones and if they are, I’m sure we’ll be in the market for them.
“At the moment it’s Manchester United next week.”
Meanwhile, concerns have been raised over Mitrovic’s temperament, with the Serbian striker picking up quickfire yellow cards against Southampton and the Swans.
McClaren, however, has likened the 20-year-old to Chelsea’s Diego Costa – and believes disciplinary action would hamper his progress.
“I’ve had a lot of these type of players during my career and you do not take that aggression, that emotion, away from the game,” he said.
“Just don’t do that. For example, Diego Costa at Chelsea. To curb it you take 50 per cent of their game away.”