ST. PETERSBURG -- Taijuan Walker felt good after throwing four innings in an extended camp game on Monday, marking another step forward in his recovery from April 2018 Tommy John surgery.

¡°Velocity was fantastic, secondary stuff, all-pitch game and felt good,¡± D-backs manager Torey Lovullo said. ¡°Just normal fatigue after the game.¡±

The right-hander allowed three runs (two earned) on three hits, struck out four and didn¡¯t walk a batter.

Alex Avila (left quadriceps strain) caught Walker on Monday and also collected a hit in three at-bats. Lovullo specifically lauded his veteran backstop¡¯s pop time on an attempted stolen base. While the next step for Avila has yet to be determined, estimates suggest he could rejoin the D-backs as soon as their next homestand, which begins Thursday.

¡°We¡¯ll reassess where [Avila¡¯s] at tonight and see what the next steps are, but we¡¯re getting a little bit closer,¡± Lovullo said. ¡°I know the hot question is, ¡®Are we going to send him out on a rehab assignment?¡¯ We¡¯re going to see it through Alex¡¯s eyes. Sometimes we don¡¯t necessarily do that for a younger player, but Alex knows what he needs. We¡¯re going to play through some scenarios.¡±

Dome, sweet dome
Monday marked the first time the D-backs had visited Tropicana Field since 2013. The indoor stadium has presented more than a few issues for visiting defenders in the past, as fly balls can be hard to make out against its white roof.

Another issue with which Arizona might have to contend is the catwalk system suspended high above the field. Many of the catwalk ¡°rings¡± are in fair territory, meaning a ball that makes contact is still considered in play.

Lovullo said beyond advanced scouting reports, veteran right fielder Adam Jones¡¯ input was invaluable. Jones would know better than most the quirks that Tropicana Field has to offer: Entering Monday, he had played 88 games in St. Pete during his 14-year career.

¡°Ball-tracking here has always been a challenge,¡± Lovullo added. ¡°Adam made some really good comments about not taking your eyes off the ball, and everybody rallied around that ball that goes in the air.

¡°You¡¯ll see our team, it¡¯s going to be a full assault on the baseball when it goes in the air, and I think we¡¯re pretty well-guided in knowing what we have to do.¡±

Designating a hitter
As suspected, Lovullo said the D-backs will take advantage of the designated hitter role during this series to squeeze in a few extra at-bats among the roster. One of the beneficiaries of the American League rules is newcomer Blake Swihart, who Lovullo said will face Tampa Bay on Tuesday or Wednesday.

Swihart, who was acquired from the Red Sox on April 19, hit his first home run with Arizona on Sunday against the Rockies.

¡°He¡¯s a good baseball player; that¡¯s the bottom line,¡± Lovullo said. ¡°I¡¯ve seen him have a lot of good moments like [Sunday]. He just needs the reps, and I¡¯m sure he¡¯s gaining more comfort here with a new ballclub and a new organization.

¡°When he¡¯s right, he can do that type of stuff. He¡¯s a very, very dependable at-bat.¡±