Porter said he told Fowler to take it slow, as it was better to miss four to five days than 15.
Fowler said he was one the bike Monday and that he had been progressing.
"I feel all right," Fowler said. "We'll just evaluate it day by day."
Fowler is batting .270 with six homers and 24 RBIs, and he had been the Astros' leadoff hitter in 33 of his 76 games. Jose Altuve has replaced him in the leadoff role.
Alex Presley has played for Fowler in center field through the four games. Porter said he did not expect that to change and that he had not considered moving George Springer back to center field, where he played in the Minor Leagues, because of the brevity of Fowler's absence.
"This is something that's not going to be an extended period of time," Porter said. "Presley has done a tremendous job in center field, and I'd rather keep George where he's at knowing that's where he's going to play the majority of the time."
Brian McTaggart is a reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. Mike Vernon is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.