Luck missed the entire 2017 season after encountering a number of setbacks in his shoulder rehab.
Colts owner Jim Irsay told reporters after practice that Luck was throwing a high school football, which is slightly smaller than what the NFL uses, according to ESPN's Adam Schefter. He added that Luck isn't expected to have any physical limitations once training camp starts.
The Colts have expressed optimism throughout the offseason that Luck will be ready to go Week 1 of the 2018 season. However, they appeared equally hopeful about Luck's chances to play in 2017 before the start of the campaign, and he wound up missing all 16 contests.
In 2016, Luck threw for 4,240 yards with 31 touchdowns and 13 interceptions. The former No. 1 overall pick went to the Pro Bowl three straight seasons from 2012-14.