CHICAGO -- The Cubs knew they would need to find additional rotation help this winter, and that situation has not changed more than two months into the offseason. In fact, Chicago's necessity for starting depth has only increased.

On Tuesday, it was learned that the Cubs released right-hander Colin Rea Monday in order to allow the pitcher to pursue an opportunity in Japan. That removes an arm that could have come into Spring Training with a fighting chance at earning the fifth spot in the rotation.

Rea had previously agreed to a one-year, $702,500 deal with the Cubs for 2021, avoiding arbitration last month.

As things stand, Chicago has right-handers Kyle Hendricks, Zach Davies and Alec Mills lined up for the top three spots in the rotation. Righty Adbert Alzolay would project as the next option for one of the remaining vacancies, with prospects Tyson Miller, Cory Abbott, Brailyn Marquez, Justin Steele and Keegan Thompson also on the 40-man roster.

Tyler Chatwood, Jon Lester and José Quintana each hit the free-agent market this offseason, taking with them 81 2/3 of the 325 rotation innings logged by the Cubs in 2020. Chicago also traded Yu Darvish (2.01 ERA in 76 innings) to the Padres this offseason in a deal that brought Davies (2.73 ERA in 69 1/3 innings), plus four prospects, into the fold.

Rea, 30, appeared in nine games (two starts) for the Cubs in 2020, logging a 5.79 ERA with 10 strikeouts and two walks in 14 innings. He went 14-4 with a 3.95 ERA in 148 innings for Triple-A Iowa in '19, which was his first full season following Tommy John surgery in November 2016.

In parts of three MLB seasons with the Padres, Marlins and Cubs, Rea has posted a 4.79 ERA with 116 strikeouts against 57 walks in 148 1/3 innings (35 games).

The Cubs are not playing at the top of the free-agent food chain this offseason, but they might look to the second- or third-tier group of available arms to help. Chicago has also not ruled out trying for a reunion with Lester, who has expressed interest in remaining with the North Siders.

"We're certainly in the free-agent market," Cubs president of baseball operations Jed Hoyer said after the Darvish trade. "It's been a slow free-agent market, but certainly we're well aware there's some holes on our roster. We lost, through free agency with Lester and Q and Chatwood, we lost three really good starting pitchers, and certainly, we're well aware of that.

"So yeah, we have some holes that we need to fill, and we're talking to agents and we're looking at free-agent signings. But it's been slow going so far. Hopefully over the next few weeks, that'll open up a little bit."