The Washington Redskins lost backup safety Tanard Jackson on Friday in a cutdown-day suspension for violating the NFL’s substance abuse policy and released Tim Hightower, last season’s starting running back who had recovered from a significant knee injury suffered in October to top the team’s preseason depth chart.

The Redskins also cut wide receiver Anthony Armstrong, the team’s second-leading receiver in 2010, Armstrong said on Twitter. Earlier in the day, the Redskins tried unsuccessfully to trade him to the Miami Dolphins for running back Steve Slaton.

As the team whittled its roster from 75 players to 53, as required by the NFL, Jackson, who was expected to see significant playing time at both safety positions, was suspended indefinitely for his third violation of the league’s drug policy, according to a statement issued by the NFL.

Jackson’s suspension begins immediately, according to the NFL, which added that he will be eligible for reinstatement Aug. 31, 2013, when his case comes up for review. Jackson, a Silver Spring native who already had lost 20 games to two previous suspensions for substance abuse violations, appealed the latest sanction but his request for a lesser penalty was denied, an NFL spokesman said.

The Redskins and Jackson’s agent, Peter Schaffer, had not commented by Friday evening.

The Redskins signed Jackson shortly after he was released by Tampa Bay in April. At the time of his release, Tampa Bay General Manager Mark Dominik said Jackson hadn’t failed any additional drug tests. Jackson had, however, failed a physical and was coming off shoulder surgery.

Jackson’s coach in Tampa Bay, Raheem Morris, was hired during the offseason to coach Washington’s secondary. When asked this summer whether the 27-year-old safety had matured, Morris said: “It’s always hard to say. You’ve got to build that thing through trust. He’s got another opportunity here, so it’s going to be his opportunity to lose or his opportunity to win.”

It’s unclear when Jackson failed his latest drug test. The Redskins were aware of his impending suspension, however, and kept five other safeties on the 53-man roster. Safe from Friday’s cuts were Brandon Meriweather and Madieu Williams, the projected starters, as well as Reed Doughty, DeJon Gomes and rookie Jordan Bernstine.

After starting training camp with an injury, Jackson had begun to progress quickly and at times looked like the most talented safety on the team. He started the third preseason game in place of Meriweather (who had suffered a sprained knee), and delivered several big hits, including one to break up a touchdown pass.

Jackson missed Monday’s practice for what Redskins Coach Mike Shanahan described as, “personal reasons,” then was held out of Wednesday’s preseason finale along with many other veterans.

The most surprising cut of the day was Hightower, who had spent the past 10 months working his way back from a torn anterior cruciate ligament suffered on Oct. 23, 2011. The fifth-year pro, whom Washington acquired via trade from Arizona in 2011, opened last season as the team’s featured back. The former Episcopal High School standout was lost for the season in the fifth game, however.

He was held out of offseason practices and was restricted to individual drills during the first three weeks of training camp. Hightower received clearance to practice fully two weeks ago, and came off the bench in the third preseason game to rush for 28 yards on five carries. He was encouraged by the outing and anticipated continued progress despite some soreness in his knee .

The pain flared up the following day, however, and Shanahan said on Monday that he was “concerned” about Hightower. The running back was held out of Wednesday’s game and he walked with a limp in the locker room and on the sideline.

Hightower’s release marked the second of a prominent Redskins player, after Tuesday’s cut of longtime tight end Chris Cooley.

The Redskins will feature a young backfield comprising second-year backs Evan Royster and Roy Helu Jr. and rookie Alfred Morris, all competing for the starting job.

The biggest victor of the day probably was third-year wideout-return specialist Brandon Banks, who entered camp after Shanahan put him on notice that he would have to prove he could help the team as a receiver and not just a kick and punt returner.

The 5-foot-7, 155-pound fan favorite got off to a rough start in the preseason, catching just two of the nine passes sent his way in the first preseason game. He didn’t get into the game as a receiver the following week. In Week 3, he returned a punt 91 yards for a touchdown, and on Wednesday he caught a 47-yard bomb and gained 43 yards on a reverse.

Banks was in competition with Armstrong, Terrence Austin, Aldrick Robinson and Dezmon Briscoe for the final two spots on the receiving unit behind Pierre Garcon, Josh Morgan, Leonard Hankerson and Santana Moss. Briscoe and Robinson, a second-year pro who spent all of last season on Washington’s practice squad, made the roster as well.

Aside from Hightower, the team cut Austin; quarterback Jonathan Crompton; offensive linemen Tom Compton, Erik Cook, Grant Garner and Willie Smith; running back Tristan Davis and tight end Richard Quinn. On defense, the team released cornerbacks Travon Bellamy and Brandyn Thompson; linebackers Brian McNally, Donnell Holt and Markus White; and linemen Delvin Johnson, Marlon Favorite, Darrion Scott and Doug Worthington.

The team was attempting to trade backup linebacker Bryan Kehl, but planned to release him if it was unsuccessful. The Redskins were negotiating an injury settlement with backup fullback Dorson Boyce, who hurt his shoulder Wednesday.