Last year's World Series MVP sprained his left thumb making a diving play against Detroit on April 9. He was slated to bat sixth.
One of the keys to Boston's AL East title last season, Lowell hit .324 with 21 homers and 120 RBIs. Before the injury, he was batting just .200 with no homers or RBIs.
"He came in and hit [Monday]," manager Terry Francona said. "We thought all along he'd be fine."
Lowell, who batted fifth for most of last season, was moved down in the order because of Kevin Youkilis' strong start.
"I told him when he went down I'd probably aggravate him," Francona said. "I was thinking of batting him seventh. Youk's been in a good groove. He's got it going. This seems to stretch out our batting order a little bit."
Youkilis is hitting .309 with two homers and 14 RBIs.
To make room for Lowell, right-hander Bryan Corey was designated for assignment.