This is likely an indication that 49ers TE George Kittle will be unable to play, as San Francisco would not have needed a tight end otherwise.
Celek, 31, wound up signing on with the 49ers as an undrafted free agent out of Michigan State back in 2012. After playing out his rookie contract, Celek returned to San Francisco on a one-year deal before signing a four-year, $14 million extension in 2016.
Celek is in the final year of that deal and set to make a base salary of $1.9 million for the 2019 season.
In 2018, Celek appeared in 15 games for the 49ers and recorded five receptions for 90 yards receiving and two touchdowns.
Johnson, 27, is a former fourth-round pick of the 49ers back in 2014. He played out the final year of his four-year, $2,620,544 contract with the 49ers before signing on with the Seahawks in 2018.
After brief stints with the Bills and Cardinals in 2018, Johnson signed on with the Chiefs this offseason. Kansas City released him in May and Johnson returned to the 49ers, only to be let go during final roster cuts.
The Chargers signed him to their active roster earlier this month only to release him when Melvin Gordon returned, making his stint in Los Angeles short-lived.
In 2017, Johnson appeared in all 16 games for the 49ers and recorded 77 tackles, one interception returned for a touchdown and seven pass defenses.