PITTSBURGH -- The Steelers open their three-day minicamp on Tuesday and it is mandatory.

Yes, that means you Troy Polamalu.

Polamalu skipped organized team activities, which are voluntary, so the veteran safety could continue his offseason training in California. The eight-time Pro Bowler is expected to take part in the three two-plus hour practices that end Thursday and conclude offseason drills.

Here are five things to watch at Steelers minicamp.

Getting to know you: Free safety Mike Mitchell, who signed a five-year, $25 million contract with the Steelers in March, is anxious to work with Polamalu. The latter had a terrific rapport with Ryan Clark, Mitchell’s predecessor, and he will need to develop some chemistry with Mitchell. That will happen during training camp, but it certainly won’t hurt that the two safeties get a feel for one another prior to the Steelers reporting to camp on July 25.

The rookie linebacker: No, not Ryan Shazier, who stood out during OTAs and is on his way to locking down the starting job at weakside inside linebacker. Sixth-round pick Jordan Zumwalt will practice with the full squad for the first time since he was not allowed to take part in OTAs because UCLA had not completed its school year. Zumwalt played both inside and outside during rookie minicamp last month and it will be interesting to see how many snaps he gets at outside linebacker. The Steelers are lacking depth at the position and there could an opportunity for Zumwalt at outside linebacker.

Jason Worilds’ participation: A nagging calf injury prevented Worilds from practicing beyond the first day of OTAs and the Steelers are likely to be cautious with their 2013 sack leader during minicamp. Worilds’ injury isn’t a concern and it gave Arthur Moats, who signed with the Steelers in March, a lot of work at left outside linebacker. But Worilds not practicing during most of the OTA sessions also showed how thin the Steelers are at outside linebacker – and how vital it is that he stays healthy this season.

Wide receiver shuffle: Markus Wheaton, who opened offseason practices with the inside track to start opposite Pro Bowler Antonio Brown in 2014, participated on a limited basis during the final week of OTAs and may be dealing with some sort of leg or foot injury. Wheaton’s limited activity provided an opportunity for Justin Brown, who spent all of last season on the practice squad, to get plenty of work with the first-team offense. Brown, Derek Moye, Darrius Heyward-Bey and Danny Coale are among the wide receivers who will likely battle for one roster spot. The real separation won’t happen until training camp and preseason games but the competition will continue at minicamp.

Sleeper watch: History says one or a couple of players who are under the radar right now will earn a spot on the 53-man roster at the end of August. Defensive tackle Al Lapuaho, a former undrafted free agent, is one player to keep an eye on. The 6-foot-2, 301-pounder, who got cut by the St. Louis Rams at the end of preseason practice in 2013, has impressed Steelers defensive end Cameron Heyward. “He’s got a good frame. He’s very intelligent and he works his tail off,” Heyward said. “We’ve got a lot of guys I want to take a look at during camp. It’s hard to [gauge the defensive linemen] right now because you don’t know how they’re going to do with their pads on but we’re off to a good start.”