Martin, 23, is a former third-round pick of the 49ers back in 2014. He’s currently in the third year of his four-year, $3.058 million contract and stands to make a base salary of $758,000 for the 2017 season.
In 2016, Martin appeared five games for the 49ers.
Mostert, 24, wound up signing on with the Eagles as an undrafted free agent out of Purdue back in May. However, he was unfortunately among the Eagles’ final roster cuts.
Mostert later caught on with the Dolphins and Ravens in brief stints before he was placed on waivers and later claimed by the Browns back in December of last year.
The Browns brought him back on a one-year, exclusive rights deal before cutting him loose. After a brief time with the Jets, the Bears signed him to their practice squad a few weeks later. However, he was cut loose last month.
San Francisco signed him to their practice squad shortly after being waived.
In 2016, Mostert has been active for two games but has not recorded a single statistic.