The Boston Celtics and Grant Williams are at an "impasse" in contract extension discussions with Monday's 6 p.m. ET deadline on the horizon, per Michael Scotto of HoopsHype.

Williams would "likely" accept an extension worth between $14-15 million per year, sources told Scotto, but the Celtics are "unlikely" to offer the 23-year-old such a deal.

“For an extension now, he’s probably in the $12-14 million territory,” an NBA executive told HoopsHype of Williams. “I think $15 million is not out of the question, but definitely on the high end, and it means they’d think he’s going to be a starter.”

Scotto's report comes after Jake Fischer of Yahoo Sports reported Wednesday that "there does not seem to be an extension coming" for Williams.

If Williams and the Celtics are unable to agree on an extension, Boston will likely extend a $6.2 million qualifying offer to the forward, making him a restricted free agent following the 2022-23 campaign.

Extending Williams a qualifying offer would allow the Celtics to match any deal opposing teams may offer him. If they don't match an offer, Williams will be moving on from Boston.

Williams emerged as a key contributor off the bench for Boston during the 2021-22 campaign, averaging 7.8 points, 3.6 rebounds and one assist in 77 games while shooting 47.5 percent from the floor and 41.1 percent from deep.

The Celtics selected Williams in the first round of the 2019 NBA draft out of Tennessee. In 209 games across three seasons, he's averaging 5.4 points, 3.0 rebounds and one assist while shooting 44.9 percent from the floor and 36.9 percent from beyond the arc.

Williams will be a sought-after free agent over the summer if he and the Celtics don't agree to terms, especially if he takes another step forward in his development during the 2022-23 season.