FOXBOROUGH – If Mac Jones can't start Sunday for the Patriots, the answer as to who'll replace him was answered on Thursday.

Backup quarterback Brian Hoyer was placed on injured reserve due to a concussion. Hoyer, who started in Week 4 in Jones' place, suffered a concussion in the second drive against the Packers on Sunday, ending his start early.

That means fourth-round rookie Bailey Zappe is in-line to be the Patriots' starting quarterback against the Detroit Lions in Week 5. Jones missed last week due to a “pretty severe” high ankle sprain. Zappe got his first official NFL action when he replaced Hoyer in Week 4. The rookie held up well in his first game. He completed 10-of-15 passes for 99 yards with a touchdown and a lost fumble in the Patriots' 27-24 overtime loss to the Packers.

After missing practice last week, Jones was back on the practice field for the second straight day Thursday. He was officially listed as a limited participant. Jones appeared to still be moving around gingerly as he took reps during the portion media was able to observe. No injury timeline was officially given on Jones' injury. Patriots coach Bill Belichick has consistently said that his starting quarterback is “day-to-day.”

Zappe's getting geared up for his first start though as we await Jones' status for Sunday's game. He said he'll rely on his veteran teammates to help on Sunday if he ends up getting the nod.

“I’m sure there will be a little bit more comfortability with it, but like I said, I’m going to lean on my teammates a lot,” the Patriots rookie said Wednesday. “They helped me a lot against the Packers and I’m going to lean on them even more this upcoming game or whenever it is. I’m really excited about just going to practice every day and get better.”

The Patriots added veteran quarterback Garrett Gilbert to its practice squad earlier in the week.

In other Patriots injury news, tight end Jonnu Smith returned to practice on Thursday after missing Wednesday's practice. He reportedly suffered a low ankle sprain that will be handled on a week-to-week basis. He was limited on Thursday. Kyle Dugger, Jakobi Meyers, Jalen Mills, and Adrian Phillips were among the eight Patriots players limited at Thursday's practice while starting defensive lineman Lawrence Guy missed practice for a second straight day.