Allen said he is balancing attempting to come back with not doing too much.
He said he returned too soon after the knee procedure in order to join his teammates in workouts the second week of September.
"When I came back the knee swelled up," he said. "The first time back I rushed it and I am trying to ease back into it."
On a team that is lacking veteran interior players, Allen, a third-year player from Pennsbury High and Temple, is expected to have a sizable role.
So far, things have gone slowly. Allen has played in four of the five preseason games and is averaging 3.5 points and 4.0 rebounds in 17.2 minutes.
In Monday's 127-97 loss to the visiting Brooklyn Nets, Allen had eight points but just one rebound and four personal fouls in 20:05.
Allen was candid when asked what positives he could take from the preseason.
"Not many," he said. "I am trying to get used to the offense and running the floor and things like that, but we've still got a little bit of time."
The Sixers open their regular season Oct. 30 at the Wells Fargo Center against the Miami Heat.
Brown is doing his best to evaluate Allen, with the understanding that there will be improvement as the knee gets stronger.
"I know he is still not 100 percent," Browns said after practice. "I am trying to help him and put him in a position where he can do well and have him understand what we need from him defensively."
Allen made his biggest contribution as a rookie during the playoffs when he averaged 6.3 points, 4.9 rebounds, and 19.7 minutes in 12 games.
Shortly afterward, he signed a two-year, $6 million contract that expires after this season.
Last season, Allen played in 79 games with 37 starts and averaged 5.8 points and 5.0 rebounds.
Allen said being sidelined during the offseason was difficult. Now he's playing catch-up.
"I was on the bike and elliptical and antigravity treadmill, but it's not the same as running the court," Allen said.
Before every practice, Allen says, he arrives a few hours early to get treatment. He is encouraged by the improvement.
"I'm feeling confident," he said.
Notes. The Sixers will hold an open practice 11 a.m. Saturday at the Palestra. The event is free and open to the public. The Sixers Dream Team and Flight Squad will perform beginning at 10 a.m.