"It was really hard to grip the bat," Alonso said before Saturday's game. "But we'll get a better look at it when we get home."
Alonso will get a scan of the hand when the team returns to Petco Park on Monday to open a three-game series against the Giants.
"I really feel I can't do the things I was doing earlier, like driving the ball," Alonso said.
Alonso said his hand hasn't felt fully healthy since before his previous injury. He hit .284 with six home runs, 29 RBIs and seven doubles in 190 at-bats before that first injury. Since then, he's hitting .278 with four doubles and 16 RBIs.
"Any time there's a hand injury, you lose some strength," said Padres manager Bud Black. "He thought that how he finished his swing, it really affected him."
The Padres reinstated first baseman/outfielder Kyle Blanks from the disabled list earlier in the day. He had been on a Minor League rehabilitation assignment with Triple-A Tucson.
Pitcher Anthony Bass was optioned to Triple-A Tucson after allowing five runs on five hits in 1 2/3 innings on Friday.
Blanks, who went on the disabled list on July 12, missed 41 games with a left Achilles injury. He was in the starting lineup on Saturday in left field, batting fifth. Jesus Guzman got the start at first base.
Blanks was 1-for-11 in four games with Tucson. He was likely going to join the team Sunday, but when Alonso left Friday's game, the team reinstated him early.
Blanks was hitting .256 with eight home runs and 34 RBIs in 67 games with the Padres at the time of his injury. He's currently wearing orthotics in his shoes to guard against future injuries.
"I've got to stay on top of [the Achilles] and stay healthy," Blanks said. "I didn't think it would be that bad, but maybe the damage was [already] done. But now I have a better idea of how to take care of it."
Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.