Jonny Evans admits he needs to continue improving after signing a new long-term contract.
The 22-year-old stopper has penned a four-year deal at Old Trafford, after becoming an integral part of the Red Devils first-team squad.
Evans, though, is not taking anything for granted and insists he needs to keep performing.
"The contract is there but you still have to perform for the manager," said Evans.
"If your performance levels dropped you could be sold in January."
Evans was linked with a move abroad with Barcelona and Real Madrid both said to be showing an interest.
But the Northern Ireland international confirmed there was no doubt about his future.
"Negotiations started a couple of months ago and went pretty smoothly," he said.
"It is a natural process. People think you go into a room, talk and it is done the next day.
"But these things take time and you just have to be patient.
"Now it is done and I am really glad to have signed."