Watt, who suffered a tibial plateau fracture to his left leg, and Mercilus, who has a torn pectoral muscle, were placed on injured reserve Wednesday.
Last season, the Texans' front seven was one of the best in the NFL and led the unit that finished first in total defense. In 2017, the Texans are tied for 19th in the league with 11 sacks.
Houston last spent time with the Chicago Bears. He signed a five-year, $35 million contract in 2014, but he tore his right ACL while celebrating a sack that season. He tore his left ACL in 2016 and has played in just 26 games over the past three seasons. Houston had a career-high eight sacks in 2015.