TAMPA, Fla. — At 35 years old, Josh McCown knows the sand is running out of his hourglass to be a starting quarterback in the NFL.

After climbing back to that position for the first time in a decade, with the Tampa Bay Buccaneers this year, he suffered a crushing setback by tearing a ligament in his right thumb during the first half of a 56-14 loss at Atlanta last Thursday night.

Even worse, the Bucs are 0-3, McCown threw two touchdowns and four interceptions and the team is preparing to play second-year pro Mike Glennon against the Pittsburgh Steelers on Sunday.

“This has been as tough a three weeks as I’ve had in my career just from a disappointment standpoint and all of that and injury and all those things,” McCown said. “But it’s not my makeup to sit and sulk. We have 13 games left. There’s a lot of football left to play.”

McCown, who signed a two-year, $10 million contract in March, has not practiced this week and will be re-evaluated. So far, he said surgery is not something he believes is required at this time.

“We take this thing day by day,” McCown said. “You know, obviously, if it was that pressing of a need, I probably would’ve already had it done. We’re very optimistic to get healthy and move forward.”

Running back Doug Martin, who missed the last two games with a knee injury, had full participation in practice again Thursday and should play in Sunday’s game vs. the Steelers.

Quarterback Mike Kafka was signed from the team’s practice squad to its 53-man roster and he is expected to dress Sunday as the backup to new starter Mike Glennon.

Guard Rishaw Johnson was waived. Johnson was acquired from the Chiefs in August for reserve safety Kelcie McCray. Johnson has been inactive for each of Tampa Bay’s three games, so he leaves the team without playing a single snap.

Center Josh Allen was signed to the practice squad. Allen was with the team in the preseason and briefly on the 53-man roster before being waived.

Players limited in practice Thursday included tight end Austin Seferian-Jenkins (ankle), defensive end Michael Johnson (ankle) and defensive tackle Gerald McCoy (hand).