[2] After being selected by the Los Angeles Rams in the sixth round of the 1985 NFL draft,[3] Johnson spent his rookie season on injured reserve due to a knee injury suffered in training camp.
In 1986, a shoulder injury kept him sidelined for most of the season before he was activated from injured reserve and played in the team's final five games, though he did not catch a pass.
Johnson's first significant playing time came when he caught six passes for 69 yards (ultimately both single-game career highs) in the Rams' 30–17 loss to the Cleveland Browns on Monday Night Football.
[4] Becoming a full-time starter at tight end, Johnson's best season came in 1988, when he caught 42 passes for 350 yards and scored six touchdowns,[5] all single-season highs for his career.
In the final game of the regular season that year, Johnson caught four passes for 42 yards and a career-high three touchdowns in a 38–16 win over the eventual Super Bowl champion San Francisco 49ers.