In a statement, the league said Goodell made the decision based on reports and recommendations from medical experts. Goodell ordered a behavioral evaluation of Roethlisberger as part of his six-game suspension under the league's conduct policy.
"The commissioner will continue to monitor Roethlisberger's progress as he begins the next phase of his recommended plan and will meet with Roethlisberger again at the appropriate time," the league said. "There has been no decision on any modification to the length of Roethlisberger's suspension."
On April 21, Goodell suspended Roethlisberger for six games, but said he would consider reducing the suspension to four games at the start of the regular season, based on the quarterback's progress.
"We look forward to having Ben rejoin his teammates on the practice field," Steelers president Art Rooney II said Thursday.
The Steelers have six offseason workouts remaining before training camp opens on July 30.
The two-time Super Bowl winner was suspended following a March incident in which a 20-year-old college student accused Roethlisberger of sexual assault in Milledgeville, Ga. The case will not be prosecuted.
If the suspension is reduced to four games, he would return for a home matchup with the Cleveland Browns on Oct. 17.
Roethlisberger is the first player suspended by Goodell under the conduct policy who hasn't been arrested or charged with a crime. When he handed down the penalty, Goodell cited a "pattern of behavior" that gave him the right to impose discipline even though no law was broken.
Roethlisberger also is being sued by a woman who accused him of raping her at a Lake Tahoe hotel-casino in 2008. He denied the allegation and wasn't charged.
Sitting out all six games would cost the two-time Super Bowl winner an estimated $2.8 million of his $102 million total contract.
In Roethlisberger's absence, the Steelers have used Byron Leftwich as the first-string quarterback in practices. Leftwich likely will be the starter for Pittsburgh in its season opener against Atlanta.
Information from ESPN NFL Insider Adam Schefter and The Associated Press was used in this report.