Friedel, 38, has kept eight clean sheets in the last 10 games to help Villa achieve the best defensive record in the top flight this season with just 18 goals conceded.
But that record will be put to the test by the Red Devils who have scored more goals than other side in the Premier League - 61 - during the current campaign including 12 in the last three games.
O'Neill said: "Can Friedel play on into his 40s? I think when you are talking about players who are advanced in years, you can judge an awful lot by immediate form.
"But I am not saying for one minute he is not capable of doing that - and I don't think for one minute he thinks he is incapable of doing it.
"It is harder to make those assessments but there is no reason why Brad can't continue this fine form for an indefinite length of time.
"If you look at David James, he must harbour strong ambitions of being the number one keeper to go to the World Cup and the two keepers are roughly the same age."
Aston Villa v Man. Utd. Click here to bet.