Berbatov has failed to make an impact at Old Trafford since joining the club from Tottenham.
Van Nistelrooy said: “I can empathise with his situation. He cost £30million, there were big expectations and they haven’t been met so far.
“He isn’t playing regularly – he plays but not always – so, of course, that’s a disappointment because expectations are sky high.
“But I think that, when he has the support of the manager and the lads, that he should just carry on and turn it around.
“I don’t think he should leave yet. This is his second year so I think that he should give it another year at least – I wouldn’t leave United that easily. I know what its like when you’ve left – when it’s gone it doesn’t come back anymore.”