Foster, who had a league-leading 55 carries over the first two weeks of the season, acknowledged Monday that he is uncertain if he will be able to return for Houston's Week 4 game against the Buffalo Bills.
"I've played through a lot in this league, and hamstrings are the hardest thing to gauge because you don't know how it's going to fatigue, how it's going to react to a certain cut," Foster said. "You've just got to let it rest ... having things heal on their own time. You can't push it or it'll relapse on you."
Foster was replaced Sunday by rookie Alfred Blue, who ran for 78 yards on 13 carries in Houston's 30-17 loss. Foster conceded it was difficult watching the game from the sideline.
"It's just hard watching your team play without you, period," Foster said, according to the Texans' website. "I put a lot into this season. I put a lot into what I do as a professional, and so do they collectively as a team.
"When all your people aren't out there, it's just hard to stomach, but it's part of the game."
The 28-year-old Foster played in just eight games during an injury-shortened 2013 season but was used heavily in Houston's first two games this year, running for 241 yards on the 55 carries while also hauling in four receptions.
Blue gained the majority of his yardage on a 46-yard run in the third quarter but struggled to produce much on the ground otherwise. Foster, however, said he was "proud" of the rookie.
"I thought [Blue] played well," Foster said. "It was his first start. I know it was on the road and he made some big plays. I feel like he has a good future in this league. I was proud of him."
The Associated Press contributed to this report.