Roberts arrived in the Rays clubhouse just before 5 p.m. ET, about 20 hours after he was officially acquired from the Diamondbacks via a trade.
Roberts hit seventh and started at third base for the Rays on Wednesday, filling a spot in the order that had been unsettled and often unproductive in Longoria's absence.
"As Longo gets well, it's nice to know that we have a player of his caliber and stature to be able to play with," Rays manager Joe Maddon said. "He'll play a lot of third base right now. He'll play some second base, he might even dabble at shortstop."
"There's other positions that he can play, also. We'll see how we're going to move it around. I'm eager to get him out there and watch it."
Wheeling a small suitcase into the visitor's clubhouse at Camden Yards just over two hours before first pitch, Roberts exchanged introductory handshakes with teammates Desmond Jennings, Sean Rodriguez and Ben Zobrist before rushing off to a meeting in Maddon's office.
"Just had a chance to visit with him, I'd only seen him on TV," Maddon said. "Real eager player, plays it hard, has a lot of tools and skills that we value."
Roberts hit .250 with six home runs, 34 RBIs and six stolen bases in 83 games for the Diamondbacks this season, playing 60 games at third with a .957 fielding percentage.
In his career, Roberts has hit .250 with 35 home runs and 134 RBIs across 390 games in seven Major League seasons.
"I know just from watching him play that he's going to like playing here," Maddon said, "because we're going to like having him play here, too."