PHILADELPHIA – Phillies general manager Matt Klentak touts Jason Vargas as a “battle-tested” left-hander who will help the rotation the final two months of the season.

Vargas certainly can't hurt.

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Vargas went 6-5 with a 4.01 ERA and a 4.71 FIP this season for the Mets, who traded him and cash on Monday to the Phillies for Double-A catcher Austin Bossart. Vargas, 36, started the season poorly, but he is 5-3 with a 3.34 ERA in 12 starts since late May.

Klentak said Vargas is expected to pitch on Friday or Saturday against the White Sox at Citizens Bank Park, but he said the team has not decided whose spot he will take in the rotation. Jake Arrieta is pitching with a bone spur in his right elbow, Zach Eflin has a 10.46 ERA in his last six starts and Vince Velasquez has a 5.00 ERA since rejoining the rotation in June.

“We’re going to consider everything,” Klentak said. “Someone could be optioned, someone could be moved to the bullpen, we could try a piggy-back. There’s a few different ways we could do it.”

Klentak said it is possible the Phillies will make more moves before Wednesday’s 4 p.m. ET Trade Deadline. In the past few weeks they added Jay Bruce, Drew Smyly and Mike Morin to the big league roster. If the Phils make more moves, they are expected to be similar deals, meaning marginal upgrades at minimal cost.

The Phillies have said they have no plans to deal top prospects because they are not just one player away from winning the World Series. But at the very least, the Phils found starting pitching help on Monday. The rotation has taken a significant step backward this season. Last season, it finished third in the National League in FIP (3.76) and WAR (15.1), according to FanGraphs. This season, it ranks last in FIP (5.05) and WAR (3.7). Phillies ace Aaron Nola is 3-1 with a 1.99 ERA in his last eight starts. The other Phillies starters have a combined 6.36 ERA in 27 starts since June 15.

“He’s been a relatively effective Major League pitcher for the better part of a decade now,” Klentak said of Vargas. “We’re trying to fortify the depth of our roster and we know that it will take more than 25 guys to win a championship. We know that it’s going to be hard to make acquisitions over the next two months, and we believe that Jason Vargas is going to give us a chance to win every time he takes the ball. That’s what he does. He keeps his team in the game.”

Vargas is making $8 million this season with an $8 million club option ($2 million buyout) for 2020. There are multiple reports that the Mets sent the Phillies $2.9 million to complete the deal. Klentak said they will wait to see how Vargas pitches before they consider the 2020 option.

The Phillies said they erred last July and August, when they traded for players that hurt the chemistry in the clubhouse. They vowed not to make the same mistake twice, saying they have performed more background work on players before acquiring them. Vargas physically threatened a reporter earlier this season, but Klentak said that is not the person he knows. Vargas and Klentak knew each other when both were with the Angels in 2013.

“When that initially happened, my first thought was, 'That was so out of character for Jason Vargas to be caught up in anything like that,'” Klentak said. “The guy that I knew in Anaheim ... it's just not who he is. He's not an overbearing personality at all like that. He's very popular in the clubhouse with everybody. He's very likable. On the mound, he's a very hard worker and a good teammate. It just didn't add up. So we did ask a lot of questions and learn a lot about that.

“I'm sure you guys will ask around -- if you haven't already -- about Jason and what his teammates and coaches think of him. You really can't find anybody to say a bad word about this guy. I think that was an isolated episode that obviously created a lot of buzz. But I don't think that was a reflection of who Jason Vargas is at all. I think it's quite the opposite. I think this guy is going to be a big plus for our clubhouse.”

Bossart, 26, slashed .195/.303/.335 with seven doubles, seven home runs and 28 RBIs with Reading. The Phillies selected him in the 14th round of the 2015 Draft out of the University of Pennsylvania.

To make room for Vargas on the 40-man roster, the Phillies designated right-hander Yacksel Ríos for assignment.

Robertson’s return sounding less likely

Right-hander David Robertson has not pitched since April because of a sore right elbow. The Phillies hoped at one point he would return by July. That will not happen. Will it happen at all this season?

“He continues to progress in his rehab at a slower rate than we had hoped,” Klentak said. “Nobody has given up hope yet, but obviously his timeline has been backed up. So we’re still hopeful that he may return sometime in August, but with each passing day it’s becoming less and less encouraging.”

Asked if that means the Phillies feel they must find a reliever before 4 p.m. on Wednesday, Klentak said, “We would like to have a rock solid eighth-inning guy to add into our bullpen mix. I’m not sure that that’s not Nick Pivetta. And I don’t want to overstate what we saw in his most recent two outings, but he looked good.”

Pivetta has struck out seven and walked one over 5 2/3 scoreless innings in his last two relief appearances, allowing just one hit.