Hargreaves sustained a hamstring injury in his first senior start in 26 months against Wolves.
“We were at the stage where we knew Owen’s knee was okay,” said Ferguson.
“His training performances for eight or nine days previously had been terrific. He had done really well, which is why we took the chance.
“But maybe the tension in the build-up for the lad was too much and he suffered because of it.”
Hargreaves’ contract at United is set to expire at the end of the season.