EAGAN, Minn. — The Vikings were back at work Monday, but it wasn't a normal day at Twin Cities Orthopedics Performance Center.

First, the Vikings put four players on the Reserve/COVID-19 List and added wide receiver Bisi Johnson to Injured Reserve.

Then, news came down that the team would not practice in pads due to a league rule.

And when it was time to practice, Vikings Head Coach Mike Zimmer wasn't pleased with how his team fared.

"They didn't practice very good today. They have to be a lot better than they were," Zimmer said on Vikings Training Camp Live. "[It was] pretty much all of it … the offense had the ball on the ground with incomplete passes and giving up sacks and things like that … milling around from drill to drill.

"Then the defense, two [practices] in a row they have a chance to win the game at the end of the fourth quarter and they give up big plays to lose the game," Zimmer added.

Kicker Riley Patterson and offensive linemen Christian Darrisaw and Cole Cabral were at practice but did not participate for the fifth straight day. Patterson is on the Active/Physically Unable to Perform List and cannot practice until taken off that list. Jeff Gladney has not been in attendance.

Offensive lineman Wyatt Davis and tight end Tyler Conklin also didn't practice. Conklin spoke to media members after practice and said his non-participation Monday was more precautionary than a problematic injury.

The team will go to full pads on Tuesday.

Here are three observations from Monday's session presented by Minnesota Eye Consultants, the Proud Ophthalmology Partner of the Minnesota Vikings:

1. A savvy vet steps up

As mentioned above, Zimmer wasn't happy with numerous facets of Monday's session. But one defensive player who did stand out was Harrison Smith.

The veteran safety picked off Jake Browning on a tipped pass and later made a diving pass breakup in a team drill.

The pair of plays highlighted a strong day for Smith, even if it was a subpar day for the defense in general. He also looked good in 1-on-1 drills in coverage on Chad Beebe over the middle.

2. Udoh goes back to tackle

With Darrisaw, Davis and Cabral out, the Vikings were down to just 12 healthy offensive linemen.

That number dropped even further as tackle Rashod Hill appeared to sit out the live reps Monday, only participating in the walk-through portion of practice. Hill watched most of practice with his position group and was holding his helmet.

That meant another position switch for Olisaemeka Udoh, who was with the first unit at left tackle despite splitting reps at right guard with Dakota Dozier so far in camp.

Dozier remained the right guard on the line with Brian O'Neill at right tackle, Garrett Bradbury at center and Ezra Cleveland left guard.

The second-team line consisted of, from left to right, Blake Brandel, Dru Samia, Mason Cole, Kyle Hinton and Evin Ksiezarczyk. Zack Bailey also saw snaps at tackle as the 11th healthy lineman.

3. Young WRs get their chance

The Vikings had two quarterbacks available Monday, which is double the amount they had Saturday.

A handful of young wide receivers made the most of it, as K.J. Osborn, Ihmir Smith-Marsette, Blake Proehl and Whop Philyor all had solid days.

Proehl, Philyor and Smith-Marsette stood out in the 1-on-1 drills mentioned above, with Smith-Marsette hauling in a long touchdown on a go route from new quarterback Chase Cookus.

Dan Chisena later had a leaping touchdown catch in a red-zone drill, and Adam Thielen followed with a diving score.