Altuve was placed on the 10-day injured list after Saturday's game, meaning Diaz is the club's primary second baseman until the three-time American League batting champion returns.
Diaz looked up to the task in Saturday's 11-4 win over the Rangers as he belted his second career grand slam. It broke open a 2-1 game to help Houston win for the seventh time in the past eight games as well as improve to 15-4 at home.
"It's tough luck for us. We need his bat in the lineup, great guy in the field," Diaz said of Altuve after Saturday night's contest. "But for me, it's my mindset to play every day and help this team win. ...
"I'm used to playing every day the past three years. We know we have a great team. My mindset is to try to be ready every day."
Diaz is batting .219 with three homers and 15 RBIs in 21 games while seeing action at five different positions.
Altuve injured the hamstring in Friday's contest. He was hopeful of avoiding a stint on the IL but came to the conclusion it was necessary after being re-examined on Saturday night.
"It's pretty frustrating but at the same time, you see how good the team is playing and that makes you want to take your time and come back 100 percent and help the team win," Altuve said. "This is not about me, this is not about one single player. This is about the team."
Houston put up a strong effort on Saturday by scoring 10 of its 11 runs with two outs.
Things aren't going so well for the Rangers, who have lost 12 of its last 17 games. Texas batters fanned 18 times and the team's runs came on Ronald Guzman's three-run homer and Hunter Pence's solo shot.
Texas manager Chris Woodward didn't downplay the importance of avoiding a four-game sweep at the hands of Houston.
"It's a huge game," Woodward said of Sunday's game. "I think every game is huge but tomorrow especially. You don't want to come out of here 0-4."
Pence is one of the few recent bright spots. He has homered in four of the past five games and has five blasts and 18 RBIs over his past 11 appearances.
Texas second baseman Rougned Odor is among the struggling players and he will get Sunday off, according to Woodward. Odor is 1-for-10 in the series to see his average drop to .137. He is just 6-for-52 with 25 strikeouts in the past 13 games.
Highly regarded right-hander Corbin Martin will be recalled Sunday by the Astros to make his major league debut. He will fill the rotation spot of right-hander Collin McHugh, who was demoted to the bullpen.
Martin, rated as Houston's fifth-best prospect by MLB Pipeline, was 1-1 with a 1.48 ERA in five appearances (four starts) for Triple-A Round Rock. The 23-year-old was a second-round draft pick in 2017.
Right-hander Adrian Sampson (0-2, 4.41 ERA) will be on the mound for the Rangers.
The 27-year-old Sampson was roughed up for five runs and seven hits over five innings in a loss to the Pittsburgh Pirates last Tuesday.
Sampson has faced the Astros twice this season, including a loss on April 1 when he gave up one run and four hits over six innings of relief. He started against Houston on April 20 and allowed two runs and seven hits over 4 1/3 innings in a no-decision.
--Field Level Media