On Wednesday, his daughter died upon delivery.
"Probably the saddest day of my life," he said.
Quarless missed the first two practices of training camp, returned on Saturday and spoke to reporters on Monday.
"I thank this team for the type of support they have given me to help me get through this," Quarless said. "Just very thankful for these guys. It's really a family in here. It's really a family.
"It felt real good just to get out there, catch some passes, be able to run around a little bit, kind of get back to your old self and get back into things. I'm looking forward to moving on in this camp and getting ready for the season."
Quarless also took to Instagram to thank his supporters during the difficult time.
Arielle Cecilia Quarless was born July 29th 2015 at 4:16pm 7 pounds 13.7 oz 21 inches.. I want to thank all my family, friends, teammates, coaches/staff, and fans for being such a support to me and my family.. My life will never be the same but with everybody's help we have been able to celebrate and honor my daughters life and this means the world to me I promise.. We were planning to have a baby instead we had an angel #GodsGifts
Quarless practiced Monday with several members of his family in attendance, including his 5-year-old son.
"He was really looking forward to being a big brother," Quarless said trying to keep his emotions in check.
Quarless was looking forward to getting back to football and thanked the Packers for sticking with him after his arrest in Miami Beach, Florida, for allegedly firing a gun in public in the early-morning hours of July 4.
He admitted that he feared the Packers might cut him after the incident and described coach Mike McCarthy as being "very upset" with him during their first conversation.
"I just apologized to him for bringing negativity to this place," Quarless said. "We have a great group of character guys. There's just so much character in this locker room. I just apologized for bringing negative because you never want to bring negative to something like this. He did tell me to just focus. Don't be too hard on yourself. As a man, you learn, you make mistakes and you learn from them. His biggest thing is to just stay focused, and I kind of took that into my training, just tried to focus on my training, trained hard and tried to come back in the best shape I can. That was my main goal."
Quarless has a court hearing scheduled for Aug. 24, the day after the Packers' preseason game at Pittsburgh.
He also could face discipline from the NFL, which already has suspended Packers defensive lineman Datone Jones one game for violating the NFL's substance-abuse policy and Letroy Guion three games after his offseason arrest for marijuana and firearm possession. Guion's suspension remains in appeal.
"It's been a lot," Quarless said. "It's been a lot. As you grow older as a man, you really understand life and you really understand things. I'm so appreciative of this team. Even from the incident earlier in the month, there's just been so much support. More than I feel like sometimes I might deserve. Just the amount of love from everybody, it's really been good for me. It's hard to explain how much that means to me. I'm just thankful.
"It really helps you put things in perspective. In my head right now, you really can't take anything for granted. Life is serious."