It meant the midfield trio were unchanged for the third game running but Milner and Keita, in their third start in eight days saw their afternoon come to a premature end.
A shocking Paul Pogba tackle resulted in Keita being stretchered off the field just after the hour mark.
Pogba would receive a red card but it leaves the Reds with dwindling options in midfield and sours what was a memorable result at the home of Liverpool’s rivals.
Following the match, Jurgen Klopp spoke of the “painful” shin injury sustained by his No. 8 after a “full throttle” tackle by Paul Pogba, a blow after a proving to be in a bright patch.
“We have to see how serious it is, it’s very painful but we’ll see – we’ll only know tomorrow or the day after tomorrow,” the manager said.
“Naby is in a great moment. He’s an outstanding player.”
On Milner, meanwhile, a hamstring injury was confirmed and he too will be set for a scan to determine the severity after going to ground midway through the first half.
“James Milner has a hamstring, he showed me something was not right,” Klopp explained.
It’s a massive blow for Liverpool who, as of full-time at Old Trafford, have Henderson, Jones and Alex Oxlade-Chamberlain as the sole senior midfielders who are fit.
Changes will come in full force on Wednesday for the League Cup trip to Preston but it’s far from an ideal situation for Klopp and co. with a further three games in the league and Champions League to follow before the November international break.