Although Washington was the team's No. 3 receiver behind Santonio Holmes and Hines Ward, his departure leaves a hole in the Super Bowl champions' offense.
"A big one," offensive coordinator Bruce Arians said on Monday night. "The guy (Washington) became a heck of a player for us. He takes the top end off the coverage. We've got to bring a young guy along.
"You always hate losing a guy you trained for three or four years, but I was happy for him. He's earned it."
Washington reportedly agreed to a six-year, $27 million contract in Tennessee.
The Steelers will have options in their search for a replacement for Washington at No. 3 receiver — including 2008 second-round draft pick Limas Sweed — but none of them will be proven commodities.
"It'll be Limas, Martin Nance and whoever we draft, one of those cats," Arians said. "Limas has the ability to do it. He just has to continue to grow and be consistent.
"He's shown the ability to get behind people and that was the No. 1 thing Nate gave us, the ability to stretch coverage."
Nance was a 6-foot-3, 212-pound, first-year pro in 2008 and was a member of the Steelers' practice squad. A former teammate of quarterback Ben Roethlisberger's at Miami, Ohio, Nance caught four passes for 33 yards in one game with Minnesota in 2006.
Sweed, 6-4, 220, caught six passes for 64 yards in the regular season as a rookie and two for 20 yards in the postseason.
His most memorable play came in the AFC Championship Game against Baltimore, when he dropped what would have been a long touchdown pass and then faked an injury in the end zone, which forced the Steelers to waste a timeout.
"Early in his career (Washington) dropped some balls, as Limas has," Arians said. "Limas gives us a bigger, more physical guy to do some blocking and some in-the-middle catching.
"I've seen him catch enough balls in practice that I know he has good hands. I think he has some focus, eye-hand coordination things that have to be worked on. Then it's just a matter of trusting your hands."
Washington caught 40 passes for 631 yards and three TDs in the 2008 regular season and seven passes for 62 yards in the playoffs.
He leaves the Steelers having caught 104 passes for 1,688 yards (an average of 16.2 yards per catch) and 12 touchdowns in regular-season play, and having won two Super Bowl rings with the Steelers.
Arians was "hoping that we could keep him, but you knew if somebody came up with big numbers (contractually) there was probably no chance."
"This is the opportunity that I waited for," Washington told the Titans' Web site Monday. "I told Coach (Jeff) Fisher earlier that I didn't want to go to a team where I felt like I needed to go there to be God. That is not the situation that I'm in now.
"This is the dream that I have been waiting for when I stepped foot on the NFL field. I'm ready for that opportunity, and I'm ready for that responsibility to step in and be a number-one type of receiver."
Washington joins a Tennessee offense that ranked No. 21 overall in 2008, seventh in rushing and 27th in passing.
"The more speed you have at all positions, the better off you are," Titans head coach Jeff Fisher told the Web site. "(Washington) clearly can run. He runs very well. He ran by a lot of good defensive players this past year. And so the speed is a bonus. But he's a football player, and that's what you need at the position. He makes catches and can get open. He's going to be productive. He can run. He understands, can get open, blocks. He does everything that you want a good receiver to do."
and you cannot have Robo because I was upset when you guys to my man Santonio.