Even when Howard hit a 423-foot home run in Friday's 5-4 win over the Braves, he said there was considerable discomfort.
"It was super stiff," Howard said. "Even at that moment it still hurt."
He said the pain worsened Saturday when he took pregame fielding practice.
"There have been times where it felt stiff before," Howard said, "but the pain and kind of stiffness, it was too much to where I knew I wouldn't be able to go out and do it and had to let them know."
Howard said that his left foot has been sore but that he would have an MRI exam only on the knee.
He had appeared in 80 games before he was placed on the DL. He is batting .266 with 11 home runs, 43 RBIs, and a .784 on base-plus-slugging percentage.
Howard said it was up to him to inform the team how his knee has been feeling.
"I think I have been pretty up-front with them," he said. "Before, there were good days and bad days. . . . On days where it wasn't feeling very well, I would always let Charlie [Manuel] and [team trainer] Scott [Sheridan] know ahead of time."
Howard said it will be good to know the extent of the injury instead of continuing to go day-to-day.
"It is somewhat of a relief," he said. "I don't know if bittersweet is the right term, but [it will be a relief] to finally be able to see what is going on and see how we want to approach it, and basically we will go from there."
Ruf in a rush
Darin Ruf was really driven to play for the Phillies on Saturday.
Ruf was in Scranton on Saturday with the Lehigh Valley IronPigs when he got the call that he would be joining the Phillies after they placed Howard on the disabled list.
"I was on my third round of batting practice and Chris Mudd, our trainer, came up to me and said to get to the Phillies as soon as possible," Ruf said.
So Ruf drove himself to Citizens Bank Park, where he arrived in the fifth inning of Saturday's 13-4 loss to the Braves. He was inserted in the game in the eighth inning and went 1 for 2 with a run scored.
A smiling star
Domonic Brown took a lighthearted approach when he was summoned to Manuel's office on Saturday to be told he had made the all-star team. General manager Ruben Amaro Jr. was also there.
"Once I got called in the office, I was thinking about trades at first," Brown joked. "Ruben made a couple of jokes, but it was cool. But like I said, it definitely was an honor."
Brown got off to a slow start. By the end of April he was batting .233 with three home runs and 11 RBIs. He had an OPS of .681.
Brown turned serious when asked if he could have imagined being an all-star earlier in the season when he was struggling.
"Oh, yes, definitely," he said. "I always tell you guys I set my goals high. This definitely was one of them and I just try to keep moving forward and improving every day."
Amaro and Manuel met with the team before the game to discuss their displeasure with Saturday's lopsided loss. . . . Catcher Erik Kratz, who underwent surgery June 12 for torn cartilage in his left knee, will begin a rehabilitation assignment Monday with triple-A Lehigh Valley. Kratz said before Sunday's game that he has been running the last few days and that the knee felt good.
The Phillies said that lefthander Jeremy Horst, who has been on the DL since June 17 with a left elbow strain, will continue his rehab assignment with Lehigh Valley.
On-base plus slugging (OPS) is a statistic that adds a player's on-base percentage and slugging percentage. The major-league average in 2012 was .724. Baseball's best hitters typically will post an .850 OPS or higher. Miguel Cabrera led the majors with a .999 OPS in 2012.