Harrison, who signed with the Lions shortly after Leshoure suffered the injury, has done well this preseason, particularly after having a few weeks to get his legs back under him.
In the preseason finale at Buffalo, Harrison led all rushers with 72 yards on seven carries including a 47-yard run that led to the Lions' only touchdown.
"Every time he goes in, he gains yards," said Head Coach Jim Schwartz after the game. "He's a very, very productive runner."
Prior to the 47-yard play, Harrison had carried the ball for five and two yards earlier in the drive.
In each of those plays, Harrison drove through the hole to claw his way to whatever he could gain. On the next play - the fourth of the drive - was when he broke for the long run.
"He's a very, very productive runner," said Schwartz. "Doesn't get thrown for too many losses and, over the last couple weeks, he's broken a lot of long runs and really done a nice job working with the team."
It has been a process of getting back into football shape for Harrison, who signed one week into training camp.
After the first two games, his production began to escalate.
Against the Patriots, he finished with 78 all-purpose yards before his 72 rushing yards this week.
"It's always fun when you get to play football, no matter who we play," said Harrison after the game. "I just went out there and played and had fun and whatever is going to happen is going to happen.