"But sending both of us very explicit death threats aimed at him, me, and our children is absolutely inexcusable."
The Indians say law enforcement has been contacted over the messages ... adding the team is investigating the threats as well.
"We continue to work through all available security channels in an ongoing attempt to identify individuals who engage in this type of behavior towards our team members and eliminate future instances," Indians officials said.
"Abusive and threatening language undermines the ability of social media platforms to create positive, healthy connections."
Wittgren has yet to pitch since Friday's game. Cleveland, meanwhile, went on to lose to the Rays again on Saturday night before beating them to close out the series on Sunday.