A floated in free-kick was controlled and finished well by Whelan on the hour mark before Maya Le Tissier levelled things up moments later, heading home from a corner as the points were shared on matchday three of the Barclays Women's Super League season.
Leicester returned to league action after a midweek victory against Liverpool in the Continental Tyres League Cup at Pirelli Stadium, but only made the once change from their previous WSL fixture, a win over Everton, with CJ Bott coming in to replace Jutta Rantala, who dropped to the bench.
Pressing high from the front, Willie Kirk's side were hoping to rob possession in the opponents' half and carve an opening through the backline. Creating a first chance when Courtney Nevin ran to the byline before picking out Janice Cayman in the box, the Belgian couldn't find the right connection and sent her first-time volley wide of the mark.
Moments later, there was another chance for City as Shannon O'Brien made some space on the left wing and picked out Whelan on the edge of the penalty area, but the captain slipped as she shot and her looping effort landed over Mary Earps' net.
The last play of the half came for Manchester United, who managed to break through the Leicester defence and get a shot away at goal, but thankfully for Janina Leitzig, Hinata Miyazawa's effort smashed the crossbar and the follow-up header was lifted onto the roof of the net.
Kirk made several changes at the break which saw forwards Hannah Cain, Deanne Rose and Rantala all introduced in an attempt to threaten the hosts' defence, and little before the hour mark, Leicester did break the deadlock.
Clever work from Cain won City a free-kick on the edge of the box which Nevin whipped into the box, eventually finding Whelan who was able to calmy fire an effort into the bottom right-hand corner past Earps, sending the Foxes into the lead with their first chance on target.
Unfortunately for the away side, this only spurred on the home side even more, and they drew back level five minutes later when a corner was headed in by Le Tissier, preventing any potential clean sheet for Leicester's defence.
Over the last 20 minutes, before a further 10 were shown by the fourth official, Leicester stood firm to continuous bombardment from the home side, and had some nervy moments when United took aim, but Leitzig, along with the rest of her defence put their bodies on the line to keep them at bay.
Academy striker Denny Draper came on to make her senior debut at Leigh Sports Village, replacing Lena Petermann in stoppage-time. Tasked with the difficult job of keeping the ball at the other end of the pitch, City's No.49 produced a hard-working cameo performance.
With the roars of the crowd growing, the referee's whistle blew, bringing an end to proceedings and confirming that Kirk's side had earned a valuable draw; taking their tally for the season up to seven points, remaining unbeaten in the 2023/24 campaign.