The Manchester United faithful were left bemused on Thursday night, as large pockets of Rangers fans found their way into home sections at Old Trafford.
The two British sides met on matchday seven of the Europa League in Manchester, with United entering the game just one point ahead of their Scottish counterparts.
Rangers were allocated 3,500 away tickets for Thursday's game, slightly more than the 3,000 accomodated for Premier League fixtures.
However, when the visitors scored a late equaliser, it became clear that a large number of 'Gers fans had found their way into the home section at Old Trafford.
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Manchester United to investigate presence of Rangers fans in home end
After Jack Butland's bizarre own-goal at the start of the second-half, it looked as though Manchester United would hold on for victory over Rangers on Thursday.
However, a late punt up the field found Cyriel Dessers, whose clinical finish drew the game level with just two minutes to spare. Strangely, some fans could be seen celebrating in the home end, revealing the presence of Rangers fans.
Footage was shared to Twitter which showed a large section of Rangers fans in a section of home fans at Old Trafford loudly cheering.
Several Manchester United supporters also took to social media to slate the club for allowing so many away fans to arrive in the home end.
A Balls.ie source in the ground on Thursday said that the atmopshere threatened to boil over in certain sections when Rangers fans celebrated their late goal.
The home fans in the home end would have the last laugh, as Bruno Fernandes scored an injury-time winner to put United on the verge of automatic qualification for the Europa League last-16.
Further footage circulated on Twitter showing the United fans giving it back to some of the Rangers fans who had brazenly celebrated Dessers' equaliser.
Manchester United confirmed that they would investigate how pockets of Rangers fans had been allowed into the home sections, though they also admitted that there is only so much they can do to prevent a recurring problem.
A spokesperson said that United ticket holders found to have passed tickets to Rangers fans would be hit with the "strongest possible sanctions":
In anticipation of the risks around tonight's game, we took the strictest possible measures to prevent sales to away fans in home areas.
Tickets were only allocated to people who existed on our database prior to the draw taking place in August. Hospitality tickets had the same restrictions applied.
Tickets forwarded by season ticket-holders and members had the same restrictions applied (i.e. they could only be forwarded to fans on our database prior to the draw).
Whilst the unauthorised touting of tickets has become more difficult since our introduction of in-app digital ticketing, it cannot be completely eliminated.
All examples of away fans in home areas will be investigated over the coming days, with the strongest possible sanctions taken against the registered holders.
This is not the first time Manchester United have encountered issues with away fan invasions at Old Trafford.
Just last season, the Champions League tie with Galatasaray saw the Turkish fans bring as many as 2,000 fans into the home section - creating a surprisingly raucous atmosphere when they took a dramatic 3-2 win on the night.
The resale system in place at Manchester United came in for criticism at the time, with some fans alleging they had donated their tickets to the club's charitable foundation only to find them in the hands of rival fans.
Though the number of away fans on Thursday was nowhere near the level of Galatasaray support found in the home end last year, it is yet another off-field moment to forget for United.
