MINNEAPOLIS -- Twins catcher Joe Mauer is likely to miss the rest of the season after being diagnosed with a mild case of pneumonia.

Mauer received the diagnosis at the Mayo Clinic on Thursday and doctors recommended medication and two weeks' rest. The Twins have 14 games remaining before the season ends on Sept. 28.

"He's really, really not happy about the situation," Minnesota manager Ron Gardenhire said before Friday's game against the Cleveland Indians. "He wants to be out there. He wants to be here with the guys, so he's pretty upset."

Mauer developed an upper respiratory infection on Sept. 2. He started medication but the symptoms persisted and then Mauer developed a cough this week while with the team in Kansas City, prompting him to visit the Mayo Clinic.

The 2009 MVP has played just 82 games this season while dealing with various injuries and was hitting .287 with three home runs and 30 RBIs. He was on the disabled list from April 14 through June 16 while he had bilateral leg weakness.

Mauer's illness just adds to the Twins' health woes. Justin Morneau has been dealing with a reoccurrence of concussion symptoms, and McWane said the first baseman also has caught a stomach bug that has been going around the team.

Third baseman Danny Valencia was in the lineup for Friday's game, but was later scratched with the flu.

Meanwhile, left-handed pitcher Francisco Liriano was going to be activated from the disabled list and be available for Friday's game out of the bullpen. Gardenhire said Liriano could receive an outing or two out of the bullpen and could start the first game of a doubleheader at Cleveland on Sept. 24.

"We'll probably start him and get two or three innings, see what happens," Gardenhire said. "Definitely a pitch count; try to get two or three innings out of him and maybe use (Brian) Duensing in there too. So we're kind of going to work our way up to that."