The 22-year-old Lansford hyper-extended his left elbow while swinging at a pitch and hasn't played since the injury. Lansford was batting .251 with four home runs and 29 RBIs through 54 games.
Puello injured his knee, McFarland said without going into detail, but returned after a night off and has appeared in each of the Hawks' last eight games. The third baseman is batting .263 in 52 games.
Lewis sprained his ankle stepping on second base, McFarland said. He has not played since the injury, but McFarland said Lewis hopes to return when the Hawks open a six-game home stand Tuesday against Spokane.
For his part, Lansford is also expected to return soon, Cubs Farm Director Oneri Fleita said.
Injuries have also affected the Hawks' pitching staff this season. Left-hander Darin Downs, a fifth-round draft pick in 2003 in his third straight season with the team, recently spent time in Arizona nursing an oblique injury.
The Hawks concluded a three-city, 11-game road trip on Sunday, defeating Yakima, 14-2. First baseman Russ Canzler hit his league-leading 15th home run, and 2006 first-round pick Tyler Colvin clubbed his sixth.
Last year's first-rounder, Mark Pawelek, picked up his third win and allowed one run on four hits in five innings, tying a season-high six strikeouts.
With nine games to play in the regular season, the Hawks hold a three-game lead in the East over Tri-City. The two team's meet for six consecutive games (a home and home series) to close out the year beginning Friday.
If the Hawks win the division, they'll meet Giants affiliate Salem-Keizer in the best-of-five league championship series. The Volcanoes have already wrapped up the Western Division with a league-best 49-18 record.
The Hawks won the Northwest League championship in 2004 and have amassed six championships total in team history.