Doctors have told the Cowboys that the injury can heal on its own, according to ESPN's Adam Schefter.
Witten ruptured his spleen against the Oakland Raiders on Aug. 13
The hope is Witten can return for Week 1 against the New York Giants on Sept. 5, but it is more likely he will return in Week 2 when the team plays at Seattle on Sept. 16.
This is good news for Dallas as their top two receivers, Miles Austin and Dez Bryant, are dealing with their own injuries. Both receivers are coping with a hamstring injury, although Austin's dates back to last season. Bryant has played in the Cowboys last two preseason games after tweaking his hamstring during training camp.
Witten is known as Cowboys quarterback Tony Romo's favorite target. For his career, Witten has 696 receptions for 7,909 yards and 41 touchdowns.
If he does miss the season opener, it will only be the second game Witten has missed in his 10-year NFL career.