The Texans improved seven games last season to finish 9-7, but missed the postseason again in large part after using four players at quarterback because of injuries and inconsistent play.
Mallett finally got a chance to start in 2014 after toiling behind Tom Brady in New England for three years. But his opportunity was short-lived because of season-ending surgery on a torn pectoral muscle after just two games. He re-signed with the Texans in the offseason
Hoyer, who signed with the Texans a day after Mallett, appeared in 14 games for Cleveland last season with 13 starts, but was benched in favor of Johnny Manziel. He threw for 3,326 yards with 12 touchdowns and 13 interceptions.
O'Brien wouldn't tip his hand whether one of them had the advantage at the end of offseason workouts. But he was impressed with what he's seen from Hoyer and Mallett so far.
''We feel very confident in both guys. We really do,'' O'Brien said. ''We have two good guys there that have really good knowledge of our system and that have both done a really good job.''
He noted that both players have gained the respect of the team and he's liked the way they've handled themselves on the field, in meetings, and in dealing with coaches and teammates.
''Both guys have shown us they can be the starter,'' O'Brien said. ''These guys command at the line of scrimmage. Both these guys know how to run an offensive huddle ... they're leaders, so I think it's helped our team.''
Here are some things to know about the Texans as they start camp on Friday:
WATT'S ENCORE: J.J. Watt is coming off a spectacular season where he had 78 tackles, 20 1/2 sacks and scored five touchdowns to win Defensive Player of the Year for the second time in his short career. But after missing the postseason for the second straight year, Watt, entering the second year of a $100 million contract, is looking to do much more in 2015.
He shared what he told the team about his expectations for himself and the rest of the Texans.
''Never be satisfied with anything,'' he said. ''Never be happy with just good. Every single day, you need to do something to make yourself better than everybody else. That's the only way we're going to improve.''
CLOWNEY'S HEALTH: Last year's top overall pick, outside linebacker Jadeveon Clowney, played just four games as a rookie because of injuries before undergoing microfracture surgery in December. His rehabilitation is going well, but he won't be on the field when training camp beings after the Texans placed him on the physically unable to perform list on Monday. They hope he can be ready for the season opener.
''He's worked extremely hard,'' O'Brien said last month. ''I think he's moving well. I think he feels better. We'll be looking forward to seeing where he is at once we get back here at the end of July.''
Watt has seen Clowney mature and is looking forward to playing alongside him.
''He's been growing as a person and I think that we're excited to get him back on the field, whenever that may be,'' Watt said. ''I think he's going to be a good addition to our team when he comes back.''
DEANDRE TAKES OVER FOR DRE: Houston's all-time leading receiver Andre Johnson was released in March before signing with the Colts, leaving DeAndre Hopkins as the team's leading receiver. Hopkins, entering his third season, had a breakout year in 2014, leading the team with 1,210 yards receiving. The Texans will use camp to see who will play with Hopkins. They signed veterans Nate Washington and Cecil Shorts III and drafted Jaelen Strong in the third round to compete for the position.
NEW CENTER: Chris Myers started the last 112 games at center before he was released this offseason. The move leaves Ben Jones to take over at what has been the team's most consistent position. The fourth-year pro will move over from guard, where he started every game last season.
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