Massaquoi and Watson were both injured in the closing minutes of the first half.
Massaquoi was hit by Seahawks cornerback Brandon Browner on an incompletion over the middle in the second quarter.
Early in the third, the team reported the injury to Watson. It's unclear when he got hurt.
Also, starting right guard Shawn Lauvao injured his right knee and coach Pat Shurmur said the second-year player will undergo an MRI on Monday.
Last season, Massaquoi missed one game with a concussion after he was hit by Pittsburgh linebacker James Harrison, who was fined for the helmet-to-helmet blow.
Information from The Associated Press contributed to this report.