Adrian Wojnarowski reports Cleveland will fish for another draft pick, but says Boston will resist the idea. (1:13)

After Cleveland's physical examination of Isaiah Thomas' injured hip raised concern about the timeline for his return this season, Cavaliers officials are planning to seek an additional trade asset before finalizing a deal to send four-time All-Star guard Kyrie Irving to the Boston Celtics, league sources said.

Without revisions to the original trade agreement, the Cavaliers could threaten to veto the trade, league sources said.

The Cavaliers' stance could trigger a standoff between Cleveland and Boston officials, forcing both organizations to weigh the consequences of letting the blockbuster trade implode.

The proposed trade sending Irving to the Celtics for two-time All-Star Thomas, forward Jae Crowder, center Ante Zizic and an unprotected 2018 first-round pick via Brooklyn was thrust into uncertainty once Thomas underwent his exam in Cleveland on Friday, league sources said. The deadline to report and submit to a physical for the players involved in the trade is 10 a.m. ET Wednesday, and the deadline to pass the physical is 10 a.m. ET Thursday, per league rules.

However, if both teams mutually agree to extend the deadline, they can. Once the sides re-engage, Cavaliers officials may try to make the case that Boston undersold them on the scope of the Thomas injury, and more specifically, how soon Thomas could be prepared to play this season, league sources said. The sides did discuss and share information on Thomas' injury, sources said.

Because Thomas is in the final year of his contract -- which coincides with LeBron James' opt-out next summer -- Cleveland has an urgency to get Thomas on the court this year.

All along, Boston has believed it was clear in its assessment of Thomas' physical status and that the information was communicated to the Cavaliers in the conversations before Tuesday's trade, league sources said. In a telephone conference call with reporters after the trade was announced, Celtics general manager Danny Ainge admitted that Thomas' physical condition played "some" role in trading him to Cleveland as part of the Irving package.

Notable Celtics Trade Assets The Celtics will have six first-round picks the next two drafts (barring protections), giving them plenty of draft capital to put in a Kyrie Irving trade. 2018 Lakers pick (ONLY if 2-5) 2018 Own pick 2019 Kings/76ers pick* (top-1 protected) 2019 Clippers pick (top-14 protected) 2019 Grizzlies pick (top-8 protected) 2019 Own pick * Only if Lakers pick does not convey

Cleveland had significantly valued the 2018 Nets pick in the trade, and Boston believed it allowed for Thomas' physical uncertainty in the current terms of the deal, league sources said.

Thomas, 28, will be an unrestricted free agent in 2018, and could still re-establish his market value with a strong performance and a return to his quick, explosive self. Cleveland had coveted 2017 No. 3 overall draft pick Jayson Tatum, but Boston has consistently remained unwilling to include him into trade talks for Irving, league sources said.

Besides its own future first-round picks, Boston has possible access to future protected picks from the Los Angeles Lakers (2018), LA Clippers (2019) and Memphis Grizzlies (2019). Boston has control of several second-round draft picks, too, which also could be included into a deal.

Irving was scheduled to take his physical with the Celtics on Saturday in Boston, league sources said. He had requested a trade from Cleveland earlier in the summer, and the possibility of finding another significant deal package without Boston's assets as leverage in the negotiations could be a sizable task for the Cavaliers.

Thomas has been rehabilitating a hip injury that ended his season in the Eastern Conference finals, and sources have told ESPN that he has yet to begin a regimen of running this offseason.

If the deal falls apart, Boston would have to count on using its arsenal of draft picks, Crowder and other assets to bring it another point guard in a future trade -- if Thomas isn't the long-term answer. Still, it is unlikely that the Celtics could find a point guard of Thomas' stature on the market -- never mind Irving's.

How Thomas and Crowder's psyches would be affected upon a vetoed trade returning them to Boston is a factor in this process too. Cleveland could be facing a bigger challenge bringing Irving, 25, back into the contentious Cavaliers situation.

He asked for a trade and has wanted no part of a return to the Cavaliers. Cleveland would need to quickly re-engage potential teams around the league on trade scenarios again. The Cavaliers could ultimately help themselves in the short term by moving Irving to one of the several Western Conference teams with whom they had discussed deals.

This way, the Cavaliers wouldn't be fortifying the biggest threat to their Eastern Conference supremacy, Boston, in the final year before James could leave in free agency. Still, Boston had offered Cleveland the deal it most wanted -- which included a draft pick that is likely better than any other available to the Cavaliers on the market.