Cubs’ Jason Hammel leaves start with hamstring injury

The Cubs’ need for starting pitching just took a potentially dramatic turn for the worse when Jason Hammel was forced to leave Wednesday night’s game after only one inning because of a left hamstring injury.

The right-hander has been one of the top performers in a rotation that has had overall success this season but lacked depth.

Hammel (5-4) ranked fifth in the National League in both opponents’ average (.212) and WHIP (0.95). His 1-2-3 first inning Thursday lowered his earned run average to 2.86.

The severity of the injury was not immediately clear. With the All-Star break starting Monday, the Cubs could back Hammel’s next start to July 20 or 21 if it’s a short-term injury.

The Cubs opened the day in wild-card playoff position, a season-high nine games over .500 and fresh off a doubleheader sweep of a Cardinals team with the best record in baseball.

The front office already had identified starting pitching as its greatest need heading toward the July 31 trading deadline. Its most recent effort to address that need was the low-cost acquisition of Clayton Richard from the Pirates.

Richard pitched well Saturday in his first big-league game in two seasons, going 6 1/3 innings for the win in a 7-2 victory over the Miami Marlins.

Richard replaced Hammel in the second inning Wednesday and gave up two runs on three hits and two walks in the second inning.