Speaking to reporters (h/t The Athletic's Vic Tafur), Gruden seemed to suggest quarterback Derek Carr was at fault.
"Cooper was open deep," Gruden said. "He was open a couple times. For whatever reason, we didn't go there."
Carr acknowledged his understanding of Gruden's offense is still a work in progress, and his coach would prefer him to throw balls away to punt rather than get hit.
"We're trying to find that line together," Carr told reporters (h/t Tafur).
Carr also struggled to find a rhythm in the Week 1 loss. He went 29-of-43 for 303 yards with no touchdowns, three interceptions and was pressured 12 times, per Pro Football Focus.
Cooper had one of the worst games of his four-year NFL career against the Rams. The two-time Pro Bowler had one reception for nine yards on just three targets. He is hoping to have a bounce-back season in 2018 after having career-lows in targets (96), receptions (48) and receiving yards (680) last year.