Ally McCoist's side extended their unbeaten third-tier run with victory over The Hedgemen yesterday afternoon, but will face the biggest test of their season when they go head-to-head with the Arabs in the Scottish Cup semi-final next month.
Rangers have a number of tried and tested top-flight stars in their ranks, but it remains to be seen if they can turn in a team performance capable of overcoming one of the best outfits in the country.
McKinnon said: "If they play like that today, they will get beaten. No doubt about it because Dundee United are a really decent side going forward. They are young, energetic, they have good players and they have goalscorers in their team.
"It is difficult for Rangers coming to places like this and raising their game week-in, week out, I get that.
"But they will need to raise their game against Dundee United and they certainly have decent enough players, enough to win the game."