The Red Devils were made to sweat in the second leg of their Europa League semi-final after Celta Vigo subjected the hosts to an uncomfortable evening at Old Trafford.
Marouane Fellaini broke the deadlock in the first half with a close-range header to give Manchester United a 2-0 aggregate lead in the semi-final clash.
However, Celta Vigo defender Facundo Roncaglia levelled the second-leg clash on the night to leave the visitors on goal away from reaching the Europa League final.
And former Manchester City striker John Guidetti missed a chance to cause an upset with the final kick of the game after Eric Bailly and Roncaglia were sent off.
Manchester United have struggled to convert their dominance into goals throughout their first season under Mourinho.
But Ferdinand is confident this is an issue that Mourinho will address in the summer transfer window.
“You need to have a team who can be ruthless and really end games in an instant,” Ferdinand told BT Sport.
“I’m sure Manchester United will be working on getting that in the summer transfer window.”
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