Valenzuela has minor-league options remaining, while backup Tyler Heineman is out of options, meaning Toronto could risk losing Heineman on waivers if they demote him.
"Kirky and Heinie worked really well last year," manager John Schneider said.
He acknowledged the team lacks depth behind Valenzuela but noted Kirk will need to build up his workload upon returning.
>>> Louis Varland Makes Strong All-Star Case for Blue Jays
Valenzuela has also earned praise from the pitching staff for his improved defense and pitch framing.
"He's getting close to Kirky's level where you think you're throwing way more strikes than maybe you are," pitcher Kevin Gausman said.
Gausman commended Valenzuela's pitch-calling and receiving, especially on fastballs in on lefties.
Infielder Ernie Clement lauded Valenzuela's power and development after the catcher recorded three hits on Saturday against the Orioles.
"He's got to be the most improved player in the big-leagues this year," Clement said.
"When he's being aggressive and swinging the bat like he has, even when he swings and misses, you hear it in the dugout, everybody's like, 'Ooh.'
That's what you want to hear."
Game Highlights and What's Next
The game also featured the return of Toronto starter Dylan Cease from a left hamstring strain. He struck out 11 batters and allowed one run over six innings.
Philadelphia starter Zack Wheeler pitched six innings, allowing one run on six hits while striking out five.
Jesus Sanchez scored Toronto's first run on a sixth-inning homer off Wheeler.
Louis Varland earned the win in relief for Toronto after giving up a tiebreaking RBI double to Bryson Stott in the top of the ninth.
Duran took the loss for Philadelphia.
>>> Don Mattingly Leads Phillies to Victory After Thomson Firing
Up next, Toronto will start right-hander Max Scherzer as he returns from the injured list on Wednesday against Philadelphia left-hander Jesus Luzardo.
