The 30-year-old rushed out to prevent Shinji Kagawa from scoring in the first half but Andre Wisdom's block on the Japan international meant that the midfielder crashed into the Spaniard and left him injured.
Reina was able to continue for the remainder of the game but missed his side's 5-0 victory over Norwich City on Saturday and boss Brendan Rodgers confirmed that he had also aggravated a thigh injury during the loss at Old Trafford.
|6/1||Liverpool are 6/1 with William Hill to finish in the Premier League top four
"He had a thigh problem before the game last week and he played and the assessment afterwards was it had got worse - plus he had broken his nose.
"He had an operation to fix the nose [on Friday] so we will see how he is by next week and review it from there."
Reina has struggled for form this season and has been put under pressure by backup keeper Jones, who came into the side and impressed during the Spaniard's absence through injury in October.
Liverpool stand seventh in the Premier League after finding form despite a troubled start to the season, six points behind fourth-placed Tottenham with 34 points from 23 games so far.