The former midfielder has also criticised the club for their transfer policy leaving them without an identity.
The former Derby County manager is enduring a difficult start to his reign at St James' Park since taking over in the summer, with his side so far failing to win in the Premier League under his stewardship.
That run of form sees them sit joint-bottom of the table alongside Sunderland, with a Capital One Cup defeat to Sheffield Wednesday having added to the pressure already on him.
And Jenas says a big problem for McClaren is the lack of character within the Magpies squad.
"Now the pressure is really on, Newcastle boss Steve McClaren is going to need some seriously strong characters in his squad to deal with it," he told BBC Sport.
"McClaren's problem is that I look at his summer signings and think character is exactly what they are lacking, along with Premier League experience and knowing how to deal with this situation."
Newcastle's transfer policy is all wrong
The former midfielder has also questioned the club’s transfer policy, with Jenas suggesting it's them without an identity.
McClaren was backed heavily in the summer transfer window by owner Mike Ashley, bringing in a number of new faces to revamp a squad that struggled to avoid relegation last season.
They have so far failed to impress collectively, though, despite their relatively big transfer fees, with fans already growing disgruntled at their summer acquisitions. And Jenas says a huge issue is that there aren’t any players on the pitch that the Newcastle faithful can relate to.
"One of the big things Newcastle have lacked over the last few years is an identity," he added.
"By that I mean players on the pitch that the fans can relate to. Their player recruitment strategy is all wrong too. They clearly needed to sign some established Premier League players over the summer, rather than taking a chance on some young talent."