Vlasic spent the 1989 off-season recovering form his injury, while the Chargers added another quarterback to the roster upon drafting Billy Joe Tolliver. After working out with the team during the preseason, he started the season on the Physically Unable to Perform list. With the Chargers having a reliable starter in Jim McMahon, who had been signed to the team, Vlasic was kept on the list for the season. In 1990, McMahon was released and John Friesz was drafted out of the University of Idaho, leaving Vlasic to compete with Friesz and David Archer for the backup quarterback job. As the preseason began for the 1990 San Diego Chargers season, the team released Archer, and the plan was for Friesz to split backup quarterback duties during the preseason. After an impressive preseason by Vlasic and only a pedestrian one by Tolliver, Chargers coach Dan Henning named Vlasic as the starting quarterback against the Dallas Cowboys in the season opener, citing that he was "steadier" than Tolliver. After losing the game 17–14, the switch was made back to Tolliver as the starting quarterback, and was eventually named starter for the rest of the season. Despite this, Vlasic remained optimistic, saying, "I feel confident in my ability, and I always have. I know I can get the job done whatever the situation. I have to believe that." Over the course of the 1990 season, Vlasic played in six games, completing 19 of 40 passes for 168 yards, one touchdown, two interceptions, and a passer rating of 46.7.