As reported yesterday, Astros' DH Evan Gattis will miss four to six weeks after surgery to repair a sports hernia. Gattis led the 2015 Astros in Home Runs despite a disappointing .246/.285/.463 stat line, ultimately providing league-average-level offensive performance. Many project Gattis to be due for some positive regression, but recovery from surgery and subsequent "rounding into shape" may make for a slow start to the season.
There is a decent-sized chance that Gattis will miss opening day, and possibly the first week or so of the major league season. He will certainly miss all or almost all of Spring Training.
Here are some options that the Astros may utilize to fill the position:
Preston Tucker: The obvious beneficiary of any absence by Gattis is Tucker, who hit .243/.297/.437 as a Rookie last season for 100 wRC+. Tucker mauled right-handed pitchers for a 120 wRC+ last season, and since he is blocked in his natural left field position by Colby Rasmus, has major league experience, some growth potential remaining, and most importantly projects to already be on the 25-man roster, Tucker seems likely to get a large portion of Gattis' missing plate appearances.
Matt Duffy: Like Tucker, Duffy is already on the 40-man roster, which will play in his favor if Gattis misses any time after the start of the regular season. Unlike Tucker, Duffy can also play third base, which may allow the Astros some flexibility, using Luis Valbuena at 1B, 3B, or DH as needed. Duffy was the Fresno Grizzlies' team MVP last season after batting .294/.366/.484.
Jon Singleton: The Astros first base apparent to start the season may benefit by receiving additional plate appearances during the spring at DH while the Astros get looks at upcoming prospect A.J. Reed.
Tyler White: Speaking of batters who have nothing left to prove in the minor leagues, Tyler White could see a large number of plate appearances this spring at the DH position, his own natural position. White blew the doors off of the PCL and Texas Leagues last season, batting a combined .325/.442/.496 including a video game-like .362/.467/.559 at AAA. White is not on the 40-man roster though, so it would take a surprising philosophy change to see him as the opening day DH to replace Gattis.
A.J. Reed: Reed is already likely to see some action in Spring Training at First Base, and the Astros' top prospect and consensus Top 50 prospect in baseball will may inherit some extra plate appearances at DH to give the Astros' coaches a good look. He will probably be sent to AAA to start the season to preserve his prospect status until after the Super Two deadline at least.
Colin Moran, J.D. Davis, Alex Bregman: Early in the spring, the Astros may want to get some looks at one of their three possible third basemen of the future. All three are non-roster invitees to Spring Training, and if they play, Luis Valbuena may shift over to DH to give them some experience at the third sack. Likewise, a little bit of playing time for outfielders Derek Fisher, Jon Kemmer, and Eury Perez may allow the Astros to give some "regulars" some time at DH to work on their timing.