Oakland Raiders head coach Jon Gruden says that wide receivers Tyrell Williams and J.J. Nelson are questionable for the Raiders' Week 5 matchup with the Chicago Bears on Sunday, according to Josh Alper of Pro Football Talk.

Williams is nursing a foot injury and has been held out of practice this week.

Should Williams not be available against the Bears, it could be a crippling blow to Oakland's offense, because he is easily the club's No. 1 receiver.

Through the first four game of the season, Williams has logged 17 catches for 216 yards and four touchdowns. The next-closest wide receiver in terms of production has been rookie Hunter Renfrow, who has recorded 11 receptions for 89 yards.

Williams was originally intended to be the Raiders' No. 2 wide out heading into 2019, but the release of Antonio Brown shortly before the season began vaulted Williams into the No. 1 role.

The 27-year-old spent the first four years of his NFL career with the Chargers, putting together one 1,000-yard season in 2016. He signed with the Raiders back in Mach.

Meanwhile, Nelson has been hampered by a knee issue and did not play during Oakland's win over the Indianapolis Colts last week. In two appearances this season, Nelson has tallied four catches for 36 yards and a touchdown.

Nelson, 27, spent his first four NFL seasons with the Arizona Cardinals, with his most productive year coming in 2016 when he caught 34 passes for 568 yards and six scores.

Oakland improved to 2-2 with its Week 4 win but will be facing a ferocious Chicago defense in London this weekend.