The St Mirren boss was left reeling after his team shipped five goals against SPL leaders Celtic last weekend.
With that hammering coming on the back of a 2-1 setback at St Johnstone, the Paisley men are now ninth in the SPL table.
With his men having triumphed in just two of their five home outings, Lennon has no doubt about the importance of a victory over Peter Houston's men.
The St Mirren manager said: "When things are not going your way you need the experienced pros in your team to stand up and be counted.
"We need them to become a focal point and allow the younger lads to rally round.
"We have some very good experienced players here like Steven Thompson, Jim Goodwin and Gary Teale who have seen it all and done it all and they have a big part to play for us right now.
"At the same time, I have challenged the youngersters like Kenny McLean and the like to show they have the self-belief and confidence to produce their best when things have not been going their way.
"It is disappointing to have dropped out of the top six, but the table is exceptionally tight, and although we are in ninth position, we are just one point off sixth.
"So a victory against United could get us comfortably back up in top six by teatime tomorrow."
However, Lennon says he has been left mystified by the individual errors that are helping to do the opposition's work for them. He has targeted a clean sheet against United as a key performance indicator on the road to recovery.
The Saints boss said: "Up until four weeks back we were pretty solid and not giving much away, but in recent weeks that has not been the case.
"Even although we won we shipped four goals against Ross County at home and we were four nil down by half-time against Celtic.
"They did not have to work hard for any of them particularly. So the focus has been on eradicating these blips and shutting the back door.
"As a team we have to tighten up as that is the foundation that will allow us to play the football we believe in.
Meanwhile, Saints' visit to Tannadice on December 29 has been moved to the following day with a 3pm kick-off.
The date was switched to avoid a clash with the game between Dundee and Aberdeen at nearby Dens Park.
