The Black Cats are still fighting to secure their Premier League safety after a mixed return to the top flight.
With three games remaining of the season, Keane admits the physical demands on some of his players may be taking its toll.
"The season is maybe catching up with some of the players.
"We are putting a lot of demands on a lot of young players, and sometimes the body just says, 'I have had enough, I need a rest'.
"It's not great timing for us, but that's what you are up against with the bigger teams with the big squads.
"You understand why those clubs have 25, 26 international players because you are going to have injuries, and they can deal with it better than clubs like ourselves.
"That's what we are trying to aim for."
Keane says the club are still a way off from establishing themselves in the Premier League, but he is optimistic for the future on Wearside.
"There is plenty (to do). If I have said it once, I have said it a million times, we just believe there is a great potential in the football club," added Keane.
"We are trying to build a football club and to maintain that and to try to keep lifting the standards, we have to stay in the Premier League, get stronger, bring in better players and keep pushing each other.
"I have not really scratched the surface.
"We are delighted with the progress the club is making and if we can stay in the Premier League this year, then we will be fairly pleased.
"But I keep saying, there is so much hard work ahead."