Niners' Bosa agrees to record-setting 5-year, $170 million deal
Shanahan told reporters he did not know the precise terms of the deal that will end the contract holdout that saw Bosa sit out training camp and the pre-season.
However, ESPN reported the extension, which includes $122.5 million in guaranteed money, will make Bosa the highest-paid defensive player in NFL history.
His average per year salary of $34 million will surpass three-time Defensive Player of the Year Aaron Donald's $31.7 million from the Los Angeles Rams.
Shanahan, who said he learned the deal had been done minutes before meeting with the media prior to practice on Wednesday, was in no doubt Bosa would be ready to play in the team's season-opener against Pittsburgh, despite missing the preparatory work.
For that not to happen, Shanahan said, "he'd need to have a beer belly and be out of shape, which is not in Bosa's DNA."
Shanahan was a little more non-commital in discussing Bosa's possible playing time.
"Knowing Nick he'll be in great shape. We'll be smart with it and base it on the next two practices," he said.
The end of Bosa's 43-day holdout bolsters the 49ers' hopes of contending for a first Super Bowl title since the 1994 season. They made it to the NFC Championship game last season, falling to the Philadelphia Eagles who were then beaten in the Super Bowl by the Kansas City Chiefs.
Bosa was scheduled to make almost $18 million on the fifth-year option of his 2019 rookie contract.
He had a career-high 18.5 quarterback sacks last season, giving him 43 since his debut in 2019 -- when he was the Defensive Rookie of the Year.
Shanahan said he did not know exactly when Bosa would join the team, because he didn't know where he was.
Bosa usually trains in the offseason at the Fort Lauderdale gym he built with his brother, Joey, a Los Angeles Chargers linebacker.