A free transfer from Arsenal last year, Obi finished the season impressively as the 17 year-old centre-forward made eight first team appearances - including seven in the Premier League.
However, so far this season, Obi has been missing from manager Ruben Amorim's plans despite the team's struggles.
Brown insists the lack of opportunity is understandable given United's overhaul of their attack this past summer, though is adamant Obi can have a big future at Old Trafford.
The former England defender told Tribalfootball.com: "I think with obviously the signing of (Matheus) Cunha and (Benjamin) Sesko, it's taken a little bit of the opportunity away, which he'll be a little bit disappointed with.
"But at the same time, he can get his head down and really work now and try and get back to where he was. But I just feel that with especially them two signings, Cunha can also going up front if needed - and so can (Bryan) Mbeumo - he's gonna have to work hard now."
Much more to come
Despite the first team path now crowded, Brown insists Obi can find his way to the first team.
He continued: "It doesn't mean it's the end of anything, but at the same time, I think those players that have just been brought in will get the opportunity a little bit more.
"But listen, everyone likes Obi and you just want him to continue the way he's going, you know, physically as well. I know he's dead tall, but believe me, I don't think he's got, um... I call it, he's not a full man yet.
"He's not got that full strength yet, and that's what he can work on, and the talent's still there and hopefully the next time we do see him, he's even stronger physically and mentally better as well."
- Wes Brown was speaking to Tribalfootball on behalf of Freebets.com