CINCINNATI -- Scooter Gennett spent a lot of time watching the Cincinnati Reds on television as his severe groin injury healed slowly over three months.

The Reds activated Gennett from the injured list Friday and had him in the lineup at second base for the opening game of a series against the National League Central-leading Cubs. Catcher Tucker Barnhart went on the 10-day injured list with a strained right oblique that is expected to sideline him for significantly longer.

A lack of offense has been the Reds' biggest problem this season. They are last in the NL Central with a .234 team batting average that's second worst in the league, ahead of San Francisco.

Until now, all Gennett could do was watch the struggles from the dugout during home games and on television while the Reds were on the road, a routine that never became comfortable.

"I'm not used to sitting at home watching baseball games, especially this time of year," Gennett said.

The biggest question is how long it will take for Gennett to become effective at the plate. He was 4-of-26 in seven games on a rehab assignment in the minors.

Gennett figures it could take some time to regain his timing, "but that's to be expected."

Manager David Bell is willing to let Gennett work out his swing while playing regularly.

"There's no question he's going to help us," Bell said. "He's a big part of our offense. He's been a big part of our offense the last couple of years."

In the past two seasons, Gennett had 50 homers and 189 RBIs, joining Dave Parker and Deron Johnson as the only Reds with such numbers in their first two years with Cincinnati. He was an All-Star for the first time last year, when he finished second to Milwaukee's Christian Yelich for the batting title at .310.

Although Gennett disliked watching games on television, he learned something by watching other hitters. Mostly, he gained a better appreciation for going to the plate with a plan for what to expect and how to approach the at-bat.

"I learned a lot," Gennett said. "I learned I need to have a plan every time, other than I see a strike and I'm going to swing."

Barnhart strained his right oblique during a swing in the batting cage this week. He won the 2017 NL Gold Glove Award in 2017. Curt Casali becomes the everyday catcher in Barnhart's absence, with Kyle Farmer -- their leading pinch hitter -- filling in on occasion. He has played four games at catcher in the majors, but none this year.

"He's done everything he can on the side to keep his skills ready," Bell said.