"We could have let him go out to Coventry, Nottingham Forest or Stoke City, the teams who enquired about him," Fergie told the clubs official website.
"But really I think it was an easy decision.
"I don't think it suits Ben entirely, but in fairness to the lad he understood."
Foster recently made his United first team debut in the 1-0 away win at Derby County because Van der Sar was injured and Kuszczak was serving a one game suspension.