Leicester City goalkeeper and former Arsenal hero both felt Juan Mata's goal should have been disallowed.
The attacker netted the team's second goal just before half-time, but the way he did so managed to upset top goalkeepers past and present.
Mata's free-kick was perfectly executed, but the presence of three United players standing offside - clearly interfering with play, distracting the goalkeeper - led to Leicester City stopper and son of Red Devils treble winner Peter, Kasper Schmeichel, venting his frustration via Twitter at the decision from the officials to allow the goal to stand.
Here is a look at what he had to say...
Massive offside!!!!!— Kasper schmeichel (@kschmeichel1) February 22, 2016
Cannot believe that wasn't given!!! Completely obscuring the keepers view therefore they are influencing play!— Kasper schmeichel (@kschmeichel1) February 22, 2016
This situation happens so often and they aren't given its unbelievable If they are anywhere within the goal frame they are interfering— Kasper schmeichel (@kschmeichel1) February 22, 2016
He was not the only one to have the same view, with ex-England international and former Arsenal great David Seaman also expressing similar sentiments via Twitter that the Shrewsbury goalkeeper was unfairly impeded.
Not happy with Man Utd second goal, 3players totally interfering with play by blocking the GK's view!! https://t.co/mYnLW3xUec— David Seaman (@thedavidseaman) February 22, 2016
The goal did not really affect the end result with United winning at a canter, but if a similar scenario had occured in a tighter contest then there would have been big controversy.
United host West Ham at Old Trafford in the next round, and the Hammers will have to be alive to any similar type of attempts from Louis van Gaal's side.