Foster, 27, who faces his former club at St Andrewâ€™s tonight, could have been in line to replace Edwin van der Sar as Unitedâ€™s No 1.
But Foster is delighted he made his Â£4million move and said: "I feel Iâ€™m back to my best. I feel good and Iâ€™m enjoying my football.
"Iâ€™m playing week in, week out and I was more than happy to come to St Andrewâ€™s.
"A club like United is cut-throat. But Iâ€™m loving it (here). I donâ€™t wish Iâ€™d stuck around at Old Trafford at all."