EARTH CITY, Mo. -- The Rams career of rookie wide receiver Bud Sasser is over before it ever got started.

The Rams released Sasser on Thursday afternoon because of a pre-existing medical condition. The team didn't disclose the nature of the problem, but league sources told ESPN.com that Sasser has a heart condition. After multiple tests, he was not physically cleared to play. Sasser was waived with a non-football-related illness designation.

The Rams signed Sasser to his rookie contract Tuesday, and he will receive his signing bonus of $113,737.

Bud Sasser had 77 catches for 1,003 yards and 12 touchdowns for Missouri in 2014. Ed Zurga/Getty Images

Rams coach Jeff Fisher confirmed that Sasser won't be playing for the Rams after the team's organized team activity on Thursday.

"We did some extensive studies after the draft, very extensive as you can imagine, and it was determined and concluded by numerous physicians that he had a pre-existing condition that we don't feel will allow him to play," Fisher said.

Sasser took the team's required physicals before last month's rookie orientation but wasn't cleared at that time. Sasser has since sought multiple opinions, but no doctor cleared him to play.

"Not in our opinion, no," Fisher said. "Not in a medical opinion and based on the medical experts and everything else. He was a non-combine guy, and that happens sometimes. Our team physicians and outside physicians recommended he not play."

Because Sasser was not invited to the combine, the Rams and the rest of the NFL were not able to put him through the rigorous physical testing that combine participants undergo. The team then circled back to the University of Missouri but did not get the information that way, either.

"We didn't have the information," Fisher said. "Typically, what you do is contact the university, and this was just one of those things that slipped through the cracks."

The Rams used a sixth-round pick on Sasser in this year's NFL draft, but he never had the opportunity to participate in a single practice. He sat out the team's rookie orientation and was not present for the start of the team's organized activities that began Tuesday.

Sasser played at Missouri, where he had 77 catches for 1,003 yards and 12 touchdowns in 2014. Despite that production, he was not invited to participate in the NFL scouting combine or any of the postseason all-star games.