Len has held off on signing any potential offer sheets and is in line to sign Phoenix's proposal at some point before Tuesday "barring an unforeseen change of events," per Wojnarowski.
By signing the offer sheet, Len can become an unrestricted free agent next offseason and would be free to sign with any team.
Phoenix selected Len with the No. 5 overall pick in the first round of the 2013 NBA draft out of Maryland, and he has slowly developed into a serviceable big.
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The 24-year-old native of Ukraine is coming off a 2016-17 season that saw him average 8.0 points, 6.6 rebounds and 1.3 blocks per game, while shooting 49.7 percent from the field.
Although he was more efficient last season, his best statistical campaign came in 2015-16 when he set career highs with 9.0 points and 7.6 rebounds per contest.
Len has shuttled between starting and coming off the bench, and he is likely to primarily be a bench player in 2017-18 with veteran Tyson Chandler serving in a starting role.
While Len will provide needed depth during the upcoming season, he may not have a long-term future in Phoenix due to the other young talent it has in the frontcourt, including Marquese Chriss, Dragan Bender and Josh Jackson.